New Jersey Department of Environmental Protection

Land Use / Land Cover Update and Impervious Surface Mapping Project



Metadata Document



In 2002, The New Jersey Department of Environmental Protection (NJ DEP) contracted Aerial Information Systems, Inc. (AIS) to revise the state’s existing GIS Land Use/Land Cover and Impervious Surface, (hereinafter referred to as LU/LC) database.  In addition, AIS was also tasked to create a new hydrology layer to replace NJ DEP’s existing hydrology data. 


The resulting LU/LC and hydrology layers are intended as a resource for trend analysis.  The layers will provide information for those who are interested in quantifying physical changes made to LU/LC features over time using GIS for their particular area of interest.  


The LU/LC update mapping began in July 2003 and was completed in September 2006.    The data compilation and conversion efforts were conducted by AIS using computer interactive photo interpretation techniques and limited on-site field surveys.  The baseline data set for the update consisted of the 1995 LU/LC data layer.  Using heads-up digitizing techniques, AIS photo interpreters compared the existing LU/LC information to year 2002 color-infrared digital orthophotography and supplemental hard-copy stereo-paired imagery, to create the 2002 LU/LC and hydrology layers.


The metadata contained herein describes for the user the methods and mapping criteria used by AIS to capture and compile the information used for the LU/LC update.  This document is divided into five sections. 


·          Section 1 includes a general description of photo interpretation methods and update mapping;


·          Section 2 lists the primary and ancillary sources of information used for the data capture, including a brief history of the baseline dataset;


·          Section 3 describes the LU/LC update methodology, criteria, and project issues;


·          Section 4 details the specific criteria used for the LU/LC update; 


·          Section 5 describes the hydrology mapping methodology, criteria, and project issues;


·          Section 6 contains the Data Dictionary; and


·          Attachment A includes the project Land Use/Land Cover and Hydrology Classification. 



SECTION 1:         General Concepts


This section contains a brief description of the basic principles of photo interpretation and update mapping. 


Photo Interpretation

Most LU/LC features can be recognized by photo signature; i.e. characteristics unique to that feature.  These signatures are defined by color, texture, pattern, and tonal qualities on the aerial photography.  By observing the extent of the photo signatures associated with specific LU/LC types, the photo interpreter is able to identify and delineate the boundaries of LU/LC features. 


When the same photo signature exists for one of more LU/LC types, the surrounding physical environment, or “context”, is an important tool in determining the appropriate LU/LC class.  Understanding current and historical patterns of development for the area results in more accurate interpretations.  For example, a large rectangular building viewed on the photo can represent either commercial or industrial land use.  Knowing that industrial uses are often located next to rail corridors and away from high traffic areas while commercial uses are usually located along major traffic corridors and intersections, the interpreter can review the surrounding environment of the building signature for those types of features.


Collateral sources are useful to the photo interpreter as they help to identify specific LU/LC features and provide a background context against which the photo signatures can be compared.  County and city street maps, USGS topographic maps, and existing vegetation maps are some of the more important sources used during the photo interpretation process.  The usefulness of existing collateral sources is directly related to the detail, accuracy, and timeliness of the information they provide.


If the above sources are not sufficient for the interpreter to confidently assign a LU/LC class, on-site field visits are required.  In addition to answering polygon specific questions flagged during the photo interpretation effort, on-site field surveys serve to verify correlations previously established between photo signatures and LU/LC types, ensuring that the interpretations are as error free as possible.   


Update Mapping

Update mapping is the process of revising the spatial and attribute data of an existing dataset using current sources of information for the purpose of change detection and trend analysis studies.   When the attributes of the finished products are analyzed in a GIS, areas of change are exposed.  Ideally the project classification, mapping criteria, and data capture method of the update should be the same as the previous data compilation effort in order to make accurate comparisons. 



The following are definitions of common terms found throughout this document. 


·         Below Resolution (BR)

This term describes LU/LC features that are smaller than the minimum mapping unit.  Below resolution features are not mapped for their specific LU/LC class but are aggregated into an adjacent above resolution LU/LC polygon.


·         Composite Coverage

Final LU/LC coverage delivered to NJ DEP containing both the 1995/97 and 2002 LU/LC delineations and codes.


·         Cowardin (FWW) Wetland

Refers to freshwater non-tidal wetland legacy polygons originally mapped for NJ DEP’s Freshwater Wetlands mapping program.


·         MMU (Minimum Mapping Unit)

The smallest polygon size (total area) mapped for each LU/LC class within a unique era.  Does not apply to polygons in the composite LU/LC coverage.


·         MMW (Minimum Mapping Width)

The smallest polygon width (linear features) mapped for each LU/LC class within a unique era.  Does not apply to polygons in the composite LU/LC coverage.


·         Polygon  

Can refer to either the polygons in the composite LU/LC coverage or the polygons created by aggregation of the LU/LC classes for a specific era.  Polygons in the composite LU/LC coverage can be smaller than the project mmu/mmw, i.e. below resolution (BR).  Unique LU/LC polygons for a specific era are typically not BR unless they are remnant polygons.    


·         Photomorphic

When the linework follows the morphology (boundary) of the photo signature.  If a LU/LC boundary follows a distinctive photo signature, the resulting polygon is said to be photomorphic 


·         Remnant polygon

Refers to existing LU/LC polygons that were above resolution but now are below resolution due to changes in the surrounding LU/LC.


·         Retroactive (Retro) Mapping

Refers to process of correcting existing 1995/97 LU/LC due to changes in mapping criteria, changes in mapping classification, image registration problems, or error of interpretation during previous update.


SECTION 2:            Data Sources


2002 Digital Orthophotography


Digital Color Infrared (CIR) orthophotos, dated 2002 and provided by NJ DEP, served as the base for both the 2002 LU/LC and hydrology mapping efforts and were used as the primary source to interpret the LU/LC, IS, and hydrology.  As with the 1995/97 Update, digital photography gives the interpreters virtually unrestricted viewing using ArcInfo tools.  This capability, in conjunction with the increased resolution and quality of the digital imagery, resulted in more accurate and detailed delineations of the data for the 2002 mapping efforts.  The orthophotos were created from year 2002 hardcopy CIR stereo imagery (see below).


2002 Stereo-paired Aerial Photography


Color Infrared (CIR) hardcopy stereoscopic photography, dated 2002 was used as a supplemental source to interpret the LU/LC, IS, and hydrology.  When stereo-paired, the imagery allowed the interpreter to see height and signature distinctions between vegetation classes, to note the general health and condition of the vegetation, and to identify topographic features on the landscape providing for more accurate interpretations of hydrology, land use, and IS cover.


1995/97 LU/LC layer


The baseline coverage for the 2002 mapping effort was the NJ DEP 1995 LU/LC coverage.  The 1995 coverage was originally compiled from three different sources: NJ DEP’s 1986 LU/LC layer (created by AIS), the Freshwater Wetlands (FWW) layer (created by NJ DEP), and the state hydrology layer (mapped by Environmental Systems Research Institute).  Prior to the 1995 update, NJ DEP converted the FWW Cowardin classes into the equivalent Anderson class.  However, in order to retain the original history of the FWW polygons, a “Cowardin” item was added to the LU/LC database and the original FWW Cowardin code was carried over for each polygon. 


1995/97 Digital Orthophotography


The digital 1995/97 CIR orthophotos that served as the base for the previous LU/LC update were used as a supplemental source of imagery for the 2002 effort.  The interpreters referred to this imagery to verify areas of change and where corrections to the existing interpretations were required.  The imagery was also used to corroborate the location of streams for the hydrology mapping effort.


Collateral Sources   

These sources were used to supplement the project imagery to help the interpreters further identify LU/LC and hydrology features.  Features on the collateral maps were compared with the imagery.  If the imagery did not support the information shown on the maps they were not delineated into the thematic layers. 


NJ Department of Transportation Road Coverage


NJ DEP provided AIS with a copy of the NJ Department of Transportation (DOT) road coverage.  This information was originally requested by AIS to help the photo interpreters distinguish dirt roads from small streams where the signature wasn’t obvious on the photo.  However, the DOT coverage did not include most of the smaller roads so this coverage proved to be of limited value during the project. 


NJ Hydrology Coverage


NJ DEP provided AIS with a copy of their existing hydrology coverage to use as reference during the hydrology mapping effort.  The coverage was used to locate previously mapped water features.  It was also used as the base for interpreting Invisible streams, i.e. streams that were not readily visible on the project photography.  


Street Maps


Current city, county, and regional hardcopy street maps, including Patton, Hagstrom, ADC, Franklin, and Geographia publications, were used to help the photo interpreters classify the land use polygons.  Although stylized in their depictions, these maps were very useful for identifying land use features, including major roads, parks, shopping malls, churches, and municipal buildings.   


USGS Digital Raster Graphic (DRG) Maps


These maps were used for determining land use, vegetation cover type, and topographic features.  Specifically, they were very helpful in the identification of utility right-of-ways, transmission line substations, small mining operations, railroads, airstrips, and other features not typically shown on street maps.  Although available for the entire state, the usefulness of these maps was limited by their age.  They are not updated on a regular basis, therefore the information is often outdated compared to the project imagery. 


SECTION 3:            LU/LC Update



The 2002 LU/LC update was performed using the same data compilation methods and essentially the same mapping classification and criteria established during the 1995/97 LU/LC update.   The state was divided into 20 Watershed Management Areas (WMAs) that were each further digitally subdivided into 1:12,000 scale quarter-quad modules based on the USGS topographic quadrangle system.  NJ DEP prioritized the mapping order for each WMA over the projected two-year schedule. Digital CIR orthophotos, dated 2002, were used as the project basemap and the State’s existing 1995/97 LU/LC coverage was used as the baseline dataset.


The photo interpreters compared the 2002 digital imagery to the existing LU/LC data and the 1995/97 digital CIR orthophotos to detect areas of change.  Using heads-up digitizing techniques, the LU/LC units were delineated and classified per the modified Anderson level III/IV classification (Attachment A).  Impervious surface values were assigned to each LU/LC unit in 5% increments based on the percentage of paved and/or built-up area within the polygon.  As in the 1995/97 LU/LC update, one acre was established as the minimum mapping unit for the project.


The 2002 LU/LC interpretations were incorporated directly into the baseline 1995/97 LU/LC coverage creating a final composite coverage containing both eras of LU/LC.  This method ensured that the different layers seamlessly co-registered to each other, creating a sliver free coverage for use in change analysis studies.


Each polygon in the composite coverage was assigned an item for 1995/97 and 2002.  Where no LU/LC change had occurred, the LU/LC class for both item years remained the same.   Where a LU/LC change did occur, the new boundaries were delineated and all of the resulting interior polygons were maintained.  Each interior polygon was coded for the appropriate 2002 LU/LC class but the original 1995/97 LU/LC class remained unchanged thus keeping the polygon “history” intact.


Project Characteristics

The following section describes significant mapping issues related to the 2002 LU/LC update.


·        Orthophoto Registration and Resolution

Theoretically the 1995/97 and 2002 digital orthophotos should have matched each other with a minimum of registration problems.  As a result, AIS was not tasked to correct LU/LC polygon boundary problems caused by image registration issues.  However the 2002 digital CIR orthophotos were significantly better in quality, exhibiting increased resolution and clarity of image.  The increase in quality provided an excellent resource for the interpretations but it also created interpretation issues because the baseline LU/LC data was created from a lesser source.  The increased resolution only served to magnify registration problems of the existing data to the LU/LC update base imagery thus creating complications in the update mapping process. 


Similar to the registration problems encountered during the 1995/97 LU/LC update (see NJ DEP 1995/97 LU/LC metadata for more information), AIS was not contractually bound to correct registration problems arising from the different sets of base imagery.   However, registration correction was vital to the objectives of update mapping in general, and specifically for trend analysis.  Therefore, AIS opted to go beyond the contracted scope of work and perform limited registration adjustments, i.e. “retroactive mapping”, for the update, in order to create a more useful tool for the State’s GIS analysis needs.  However, unlike the 1995/97 LU/LC project, the retroactive registration adjustments were also performed on legacy FWW polygons per NJ DEP’s mapping criteria (see Section 4 of this document). 


·        Archived 1986 LU/LC Data

Unlike the 2002 and the 1995/97 LU/LC update, the 1986 LU/LC layer was created using photo interpretation and manual cartographic techniques.  CIR stereo-paired imagery, dated 1986, was interpreted through a stereoscope while polygons were drafted onto a mylar overlay registered to a 1:24,000 black and white orthophoto basemap.  The LU/LC features were classified using a modified Anderson Level II/III classification.  The minimum mapping unit was 2.5 acres. 


Concurrent with the 1986 LU/LC compilation, NJ DEP also created their Freshwater Wetlands (FWW) coverage and updated their statewide hydrology.  Both mapping projects were performed using hardcopy black and white orthophoto basemaps and the same CIR imagery used for the 1986 LU/LC mapping. NJ DEP merged the 1986 LU/LC, FWW, and hydrology coverages into a single GIS dataset that formed the basis for the 1995/97 LU/LC update.  During the merging process, the FWW layer took precedence over the hydrology layer, which in turn took precedence over the 1986 LU/LC layer.  


At the start of the 2002 project, the 1986 data layer was originally included as part of the updated coverage along with the baseline 1995/97 information.  However, registration problems between the 1986 data and the 2002 imagery created a significant amount of meaningless sliver polygons in the dataset that potentially could interfere with meaningful trend analysis studies.


Due to this issue and the age of the original LU/LC data, NJ DEP decided to archive the 1986 LU/LC dataset and it was removed from the 2002 LU/LC update mapping project.  As a result, retroactive mapping edits caused by registration problems or changes to the 2002 classification or criteria were not applied to the 1986 data but only to the 1995/97 LU/LC layer.   


·        New and Redefined 2002 LU/LC Codes

Several new codes were added to NJ DEP’s existing LU/LC classification for the 2002 update.  In addition, some definitions for existing codes were modified to better suit NJ DEP’s current modeling needs.  AIS and NJ DEP collaborated on defining the class descriptions and refining the mapping criteria, as needed, for existing classes.


While most of the new codes were added prior to the start of the LU/LC interpretations, some of the additions occurred after the production phase of the LU/LC interpretations had commenced.  While AIS made the maximum effort possible, including re-reviewing previously mapped data, to correctly represent the late criteria and coding additions and revisions, the User is advised that potential inconsistencies of interpretation could exist in areas mapped prior to the addition/revision date for the new codes. 


Listed below are the new Anderson classes for the 2002 LU/LC update, the date added, and other pertinent information.  For a full description of the codes, please refer to Amendment A, included at the end of this document.


1410     Major Roadway

1419     Bridge Over Water

1440     Airport Facilities

1461     Wetland Rights-of-Way

1462     Upland Rights-of-Way, maintained

1463     Upland Rights-of-Way, non-maintained

1499     Stormwater Basin

1710     Upland Cemetery

1711     Wetland Cemetery


1741     Phragmites Dominate Urban Area

1810     Stadiums, Theatres, Cultural Centers, and Zoos

2140     Agricultural Wetlands

2200     Orchards, Vineyards, Nurseries, and Horticultural Areas

4411     Phragmites Dominate Old Field

6110     Saline Marshes

6111     Low Saline Marsh

6112     High Saline Marsh

6113     Phragmites

6141     Phragmites Dominate Coastal Wetlands

6241     Phragmites Dominate Interior Wetlands

7500     Transitional Areas


·        Legacy Freshwater Wetlands (FWW) Wetland Polygons

Most non-tidal wetland polygons in this project were derived from New Jersey’s Freshwater Wetlands (FWW) mapping program.  NJ DEP created the FWW coverage during the 1980s.  The FWW program mapped non-tidal wetlands and water bodies using the National Wetlands Inventory Cowardin classification for wetlands above NJ DEP’s Upper Wetlands Boundary (UWB) line. 


Prior to the 1995/97 LU/LC mapping effort, the FWW information was merged with the 1986 LU/LC and the State’s hydrology layers, with the FWW information taking precedence, to create the baseline dataset for the 1995/97 LU/LC update.  NJ DEP converted the FWW Cowardin classes into the appropriate Anderson LU/LC class.  The original Cowardin codes were carried over into the LU/LC data by adding a Cowardin item to the data structure. 


In 1995/97 data from the FWW program was in active use at the state level for permitting, development, and other environmental uses. To ensure the integrity of the wetlands delineations NJ DEP implemented strict LU/LC mapping criteria.  The new criteria were very restrictive, preventing the interpreters from altering the FWW polygon boundaries or codes unless the wetland had been physically altered.  As a result, registration problems and interpretive errors were not corrected for the FWW polygons in the 1995/97 LU/LC dataset.


The 1995/97 criteria were carried into the 2002 mapping effort and remained in effect until September of 2004.  NJ DEP completed their review of the first 2002 LU/LC data delivery in August of 2004 and were not satisfied with the wetland delineations.  After reviewing their options, NJ DEP concluded it was more important to make the wetland boundaries and codes match the 2002 orthophotos rather than maintain the integrity of an increasingly out-dated dataset. 


Per NJ DEP’s request, the existing criteria were revised to allow the photo interpreters to correct FWW wetland registration and interpretation errors resulting in a more accurate representation of the wetlands in 2002.  The original Cowardin codes were transferred to all corrected wetland polygons to maintain a legacy FWW presence within the LU/LC layer. 


The wetland criteria change was implemented after a significant portion of the LU/LC Update had been performed.  Although the change represented an increase to the project scope of work, AIS agreed perform the remainder of the LU/LC update using the new criteria.  AIS also agreed to revisit selected priority watersheds that had already been updated and retroactively implement the new mapping criteria.  NJ DEP was responsible for updating non-priority watersheds that had already been mapped.   


·        Photo Signature versus On-Site Field Observations

The user should be aware that the data represents LU/LC as it existed at the date of the project photography, with some exceptions.  In general, if subsequent on-site field surveys revealed that the LU/LC had changed since the 2002 photography, the polygon was coded for the 2002 photo signature, not the LU/LC observed in the field. Therefore, although the project photography is relatively current, the information available for LU/LC interpretation will be a minimum of three years old at the time of project completion. 



The following outlines the basic procedures used for the update mapping effort.  These are general in nature and grew out of the unique characteristics of the project.  Specific criteria of the project are discussed later in Section 4. 


  1. Registration – A substantial portion of the linework from the 1995/97 update was corrected during the 2002 LU/LC update to reflect the considerably superior photography.  This included the linework of both FWW and non-FWW polygons.
  2. Comparison – concurrent with the registration, the 2002 photography was compared to the baseline data and the 1995/97 photos for LU/LC feature changes. 
  3. Delineation – Areas of change were added or removed from polygons, while existing features not previously delineated, or delineated incorrectly were retroactively mapped.   
  4. Classification – Each polygon in the 2002 data was coded for the appropriate Anderson level III or IV category, in accordance with the classification discussed in Attachment A. 
  5. Impervious Surfaces – Each LU/LC feature was assigned an IS percentage, ranging from 0 – 100, in increments of 5%, based upon the estimate of experienced photo interpreters.  
  6. Edgematching – The working modules, when completed, were edgematched to adjacent modules for consistency of polygon delineations and coding. As all of the modules within a WMA were completed, the WMAs were edgematched to each other to create a seamless statewide dataset. 
  7. Field Verification and Revision were performed in conjunction with the photo interpretation to ensure that the data produced was as error free as possible. Field plots containing the project imagery and preliminary LU/LC delineations were created and prepped with street names and daily routes. Polygons flagged for field were reviewed on-site, if possible, and resolved. Additional verification of non-flagged polygons occurred to ensure the accuracy of established correlations between photo signatures and specific LU/LC feature types. Upon return to the office, the interpreters entered the field corrections and changes directly into the 2002 LU/LC dataset.  


Upon completion of these seven steps for each WMA, a preliminary ArcInfo coverage of the data was delivered to NJ DEP for review.  If necessary, revisions were made to the dataset per NJ DEP comments.  The coverage was considered final when all of the adjacent WMAs had been mapped and edgematched across WMA boundaries, and all necessary revisions had been made.




SECTION 4:      General LU/LC Mapping Criteria




This section describes the final criteria as developed by AIS and NJ DEP.  Many of these criteria were developed over the course of the project in response to new situations or to modify existing situations.  As the procedures evolved they were submitted to NJ DEP for approval.  Any discrepancies in mapping procedure from the beginning of this project to the end were due to this evolution, and were recognized by both AIS and NJ DEP. 


These criteria supersede all previous criteria for this project.  


Drafting Conventions

The following details the drafting criteria used to delineate the LU/LC units. 


General Drafting Criteria


·          When a road separated differing LU/LC features, the polygons for these features followed the road centerline.  Although roads often include a right-of-way on either side, these slivers of land between the roads and the adjacent LU/LC features were aggregated with the LU/LC unless they could be reasonably extracted.  The above criteria were applied for the delineation of new LU/LC polygons.  Existing LU/LC polygon boundaries that did not follow road centerlines due to image registration issues were not corrected.   


·          Where roads and features on the orthophoto differed from those represented on other collateral sources, the location on the orthophoto was used to depict the feature.


·          Boundaries are followed as closely as possible.  Where boundaries were particularly jagged, however, some cartographic smoothing was deemed appropriate.  This was generally for use along natural boundaries and was rarely needed along man-made boundaries. 


Urban/Built-Up Areas


Built-up land uses usually follow man-made features such as fence lines, roads, and property boundaries.  To properly represent these boundaries: 


·          Linework was kept straight and used right angle corners.

·          Lines were placed down the centerline of boundaries (such as roads, railroads, and tree lines).

·          Structures were not dissected.


Non-Urban/Natural Areas


Natural vegetation boundaries tend to be transitional therefore the line separating different classes is often less distinct.  These polygons seldom contained straight edges or angles unless the vegetation unit was adjacent to built-up or man-made features.  Vegetation category polygons were usually represented with flowing and curvilinear lines, reflecting the more natural shape of the land cover. 



Minimum Mapping Unit/Width

The minimum mapping unit for the 2002 LU/LC was established at one acre for all features.  Additionally, a minimum width of 60’ was required for non-water linear features, such as transmission lines, roads, etc., while a minimum width of 30’ was required for water.


The following aggregation guidelines were compiled for below-MMU LU/LC features and polygons. 


·          Built-up land uses took precedence over non-built up categories.  For example, if a below-MMU residential land use was adjacent to a below-MMU forest cover, the forested area was absorbed into the residential land use. 


·          In general, residential land uses took precedence over other built-up land uses.  If a below-MMU residential land use was adjacent to a below-MMU commercial land use, the commercial area was absorbed into the residential land use. 


·          If a below-MMU LU/LC feature was surrounded by a number of other above-MMU LU/LC features, then the below-MMU unit would be absorbed into the unit that most closely represented its class.  For example, if a below-MMU residential class was next to above-MMU commercial, industrial, and forested polygons, the residential land use was absorbed into the commercial polygon. 


·          An isolated below-MMU LU/LC feature completely surrounded by a single LU/LC feature was absorbed into the surrounding LU/LC class. 


·          Some remnant polygons remaining from 1995/97 Update were merged according to the criteria above if they were not significant to the overall classification of the area. 


Below-MMU polygons were left intact or created in the following situations: 


·          Isolated below-MMU roads completely surrounded by FWW wetlands were left as is. 


·          Some LU/LC features were mapped even if below-MMU and isolated, provided they were significant to the overall classification of the area.  If the 1.0-acre MMU had been strictly observed, these units would not have been captured in the database.  By mapping certain LU/LC classes smaller than the 1.0 acre MMU, the user is given a more accurate depiction of LU/LC conditions in these areas. 


·          Remnant polygons from the 1995/97 Update were kept provided they were significant to the overall classification of the area.  Typically these included built-up land uses and wetland vegetation types.  Upland vegetation remnants were usually re-classified into surrounding LU/LC polygons.  


·          When an unchanged FWW wetland incorrectly included existing paved or otherwise disturbed areas, said areas were delineated out of the wetland polygon and aggregated with the adjacent LU/LC class. This process sometimes resulted in below-MMU wetland polygons that were left over after the disturbed/built-up land use was coded out of them.


Retroactive Mapping

Retroactive mapping was defined as any correction to the existing LU/LC data due to changes in classification, criteria, registration issues, or error in the original photo interpretations.  To qualify for retro mapping, the photo signature in 2002 and 1995/97 had to be the same, i.e. no detectable change in LU/LC, and the corrections had to comply with the 2002 mapping criteria.


General Retroactive Mapping Criteria (Cowardin and non-Cowardin LU/LC)


·         Polygons improperly coded during the 1995/97 effort were reassigned the appropriate LU/LC values for the 2002 update.  These values were then retro-mapped back to the 1995/97 data.


·         Polygons improperly coded as a result of the differences in criteria between the 1995/97 and the 2002 updates were given the appropriate code in 2002.  It was then retro-mapped to the 1995/97 data set.


·         Features on the imagery meeting minimum mapping unit but not delineated due to photo interpretation error in 1995 were pulled out and retro-mapped.


Non-Cowardin Wetland Retroactive Mapping Criteria


·         Any or all portions of linework that were determined to be inaccurate were deleted and then re-delineated to correlate with the 2002 imagery.


Cowardin Retroactive Mapping Criteria


·         Since the Cowardin wetland delineations were not corrected for registration issues or possible interpretation errors during the 1995/97 update, many of the Cowardin wetland boundaries were not consistent with the 2002 imagery.  Per the 2002 FWW legacy criteria, retroactive mapping of Cowardin wetlands allowed for the correction of registration and coding errors yet still retained the integrity of the original FWW delineations.  To achieve this, the interpreters subdivided or added to the original wetland units without deleting the original linework and retained the original Cowardin class as part of the polygon history.  When the distance was insignificant between the polygon boundary and the correct location on the 2002 image, the polygon boundary was simply adjusted.


·         Wetland polygons containing existing built-up or paved areas were re-delineated if the non-wetland areas were above-MMU or capable of being aggregated.  Any new polygons were then retro-mapped back to 1995/97.


·         Polygons containing below-MMU wetlands adjacent to polygons of like land use were retro-mapped to re-aggregate the below-MMU wetland with the more appropriate LU/LC class, using the FWW legacy mapping criteria.  For example, where upland agriculture (2100) was adjacent to a wetland deciduous tree polygon (6210) that included a BR wetland agriculture signature, the wetland agriculture was delineated out of the 6210 as a separate polygon.  The LU/LC class was then changed to 2100 and retro-mapped back to 1995/97 but the original Cowardin wetland class for the 6210 was retained in the new polygon history.


Criteria Changes from 1995/97 for the 2002 Update

The 2002 LU/LC update retained most of the criteria used for the 1995/97 mapping effort.  However, there were criteria changes resulting from the addition of new codes and the redefinition of existing codes.  The major criteria changes are shown below.



In 2002, the 1400 code was retained for categories such as local roads, railroads and maintenance yards; however, it was also sub-divided up to represent a group of new categories featured in the update effort. The following is a description of the criteria that accompanies these new codes.  A complete list of said codes in the 1400 class can be found in the corresponding “new codes” section of this document.


·         1410

Major Roads were taken out of the 1400 class and put into the new 1410 code and defined as major roadway rather than the Anderson limited access road.  Areas on the imagery where railroads and highways ran parallel and adjacent were delineated as 1400 to indicate the presence of two types of transportation, rather than being coded out as 1410.  In the final version, DEP identified minor roadways and railroads and coded them as 1400.  The IS%, however, is much lower for railroad transportation corridors than roadways, generally less than 15%.


·         1419

Bridge over water, which were not delineated in the previous update, were given a 1419 code and defined as the intersection between polygonal or linear water features and major highways or railroads.  The 1419 code indicates the presence of a water feature and bridge feature essentially sharing the same space on the imagery; it takes precedence over the 1400, 1410 code and the 5000 class.


·         1462 and 1463

Utility rights-of-way were also introduced as separate categories in the 2002 update.  Initially in the project 1462 was defined as “non-maintained” while 1463 was defined as “maintained;” however, as the mapping effort progressed, this definition was reversed.  Finally, 1461, 1462, and 1463 were expanded to include non-electrical rights-of-way as well.  In this study, rights-of-way were absorbed with adjacent land uses unless they achieved a width of sixty feet, in which case they would be pulled out and labeled with the appropriate right-of-way code.  Rights-of-way take precedence over all land cover, but will not be pulled out when traversing land use except for the 1700 category.


·         1499

Stormwater basins are also a new category in 2002.  Like the rights-of-way category, their coding also underwent a sort of evolution during the mapping process.  For upland polygons existing within drainage basin boundaries, the initial coding evolved from 1400 to 4410 to 1700.  When FWW polygons existed within drainage boundaries, either alone or in conjunction with upland polygons, they were initially coded as 1750.  When the codes were assigned in this manner, two below-resolution polygons were allowed to co-exist if together they made up a > 1-acre stormwater basin.  Ultimately it was decided that all polygons comprising drainage basins would be coded as 1499 and retro-mapped back to 1995.  This category takes precedence over all land cover and non-built up land use categories (such as 1700 and 2100).  It also takes precedence over rights-of-way.  



The 1700 class was subdivided to classify upland cemeteries as a separate class.  Otherwise the 1700 category remained unchanged for the 2002 update.  Any other open areas maintained as part of transportation corridors which are primarily open, were included as 1700.  Where roads dominate the polygon the codes were more likely to be 1400.


·         1710 and 1711

Cemeteries were initially delineated separately from the 1700 code for the first time as 1710 for upland cemetery and 1750 (defined as managed wetland) for wetland cemetery.  The 1710 code was retained for the duration of the mapping effort but the 1711 (wetland cemetery) class was added during the production process. 


Other criteria changes related to cemeteries include the order of precedence.  In 1995/97, below-resolution churches adjacent to below-resolution cemeteries took precedence over the cemeteries, resulting in a polygon coded as 1200 rather than 1700.  In the 2002 update, however, this reversed and the cemetery code took precedence over associated churches and vegetation if aggregation was necessary for accurate delineation.



Wetland cemetery polygons, originally coded as 1750, were reclassified as 1711 (see the entry above for specific criteria).  Otherwise the 1750 criteria/class remained unchanged from 1995/97.  



The 1800 class was expanded in 2002 to include a new code, 1810, for stadiums, theaters, cultural centers, and zoos.  The 1810 class was only mapped where collateral sources identified the location or the photo signature was obvious.   



The 2140 category definition was expanded in 2002 to include cranberry bogs/farms.   The 1995/97 dataset initially depicted the upland portion of cranberry farms as 2200 while the wetland portions (FWW polygons) were captured as an inconsistent mix of natural vegetation (62xx), water (5300) and wetland agriculture (2140).  After much discussion with NJ DEP, the final criteria defined all land (upland and wetlands) and water within the boundaries of the bogs as 2140; while non-dyked water was kept as 5300.



In order to maintain a consistent representation of water polygons between the LU/LC and hydrology coverages, the LU/LC minimum mapping width (mmw) of 60’ was changed to match the hydrology mmw of 30’. The total area minimum mapping unit for both the LU/LC and hydrology remained at one acre.  As a result, many polygonal streams that were below resolution for the 1995/97 LU/LC update were captured in the 2002 dataset and retroactively mapped back to 1995/97.


If the “new” stream delineations connected to an existing FWW stream polygon, the individual polygons defining the stream were merged together and the original FWW Cowardin code was retained in the polygon.  Where the stream delineations did not connect to an existing FWW stream polygon, the individual polygons defining the stream were merged into one and the polygon was coded as 5100 without a Cowardin class.  When the stream delineations cut through existing non-water FWW polygons, the polygons were merged into one and coded as 5100 without retaining the FWW history.  This is an exception to the FWW legacy mapping criteria.



The coastline of the Atlantic Ocean was also clarified to pull out portions of the sandbar that had expanded significantly.  For this project, this expansion was defined as greater than sixty feet in width, and was mapped as change when applicable.



This class was expanded during the 2002 mapping effort to include two new sub-categories of saline marsh and a separate class for Phragmites. 


·         6111

The 6111 code, referred to as low saline marsh, was defined in 2002 as areas of brackish wetland lying in close proximity to the ocean.  This category of marsh was also determined to be inundated at least once a day, and therefore maintained a very low vegetation cover, usually not exceeding 1 foot in height.  6111 retained the 6110 code in 1995/97.


·         6112

The 6112 code, defined as high saline marsh, was defined as lying further inland than 6111 but close enough that it was inundated typically 1-2 times per month.  This code reflected areas that sustained vegetation layers between 1 foot and 3 feet in height.  6112 also retained the 6110 code in 1995/97.


·         6113

The 6113 code was defined as portions of the imagery dominated by the invasive grass species known as Phragmites.  While Phragmites was typically found in wetland environments, it was also capable of sustaining itself in upland environments.  It was characterized by a low, smooth, circular signature that ranged in color from white to dark grey.  Phragmites retained the 6110 code in 1995/97 when it was identified in a saline marsh environment; if located elsewhere, it retained the 1995/97 code for that particular area.  DEP reclassified all 6113 codes to one of 4 codes (1741, 4411, 6141, 6241) depending on the 1995/97 coding and interpretation.


62xx - FWW (Cowardin) Wetlands

When the project was in its beginning stages, the contract called for adherence to the criteria set during the 1995/97 mapping effort.  These criteria called for registration problems occurring in the dataset to be ignored if unaccompanied by change or photo interpretation error in need of retroactive mapping.  Fresh water wetlands (FWW) polygons were particularly restricted; the code could not be altered unless change had occurred, and the integrity of the original linework had to be maintained.


It soon became clear, however, that the photography used in the 2002 update was of incredibly high quality, highlighting the already obvious discrepancies occurring between the linework and the imagery.  Although the process of registration correction is a time-consuming and therefore expensive undertaking, the final product would have been far less successful as a trend analysis tool if no registration corrections were made.  Over the next year, AIS and the NJDEP worked together to come to a decision regarding how to approach this issue.


WMA 9 was the first watershed delivered to NJ DEP in the summer of 2004.  After reviewing the data, NJ DEP requested that a new criteria set be developed regarding the FWW wetlands.  This request was made after a large portion of modules had been photo interpreted and/or quality controlled based on the 1995/97 criteria. 


AIS agreed to the changes and updated WMA 9 using the new criteria.  The resulting dataset fit very well with the imagery but the amount of time taken to complete the watershed was staggering.  AIS and NJ DEP agreed that AIS would map/remap the majority of the WMAs to the new criteria but that NJ DEP would be responsible for updating the previously mapped WMAs 14, 15, and 19 to the new rules. 



Impervious Surfaces Mapping (IS)


Relationships between land uses and impervious surfaces previously established by the National Resource Conversation Service were used as baseline values for the built-up land use categories.  Values were estimated based upon the percentage of impervious surfaces within a given polygon. 

·          IS was interpreted in 5% increments, from 0% to 100%.


·          Impervious surface percentages were assigned to each LU/LC unit based on an eyeball estimate of the paved and/or built-up area within the polygon.


·          Where a single LU/LC polygon contained areas of differing IS and each area met the 1- acre MMU, the polygon was subdivided and assigned different IS values.


·          All built-up and/or paved land uses were mapped as impervious surfaces and assigned IS values greater than 0%.


·          Hard packed earthen areas (earthen dams excepted), gravel areas, and natural rock areas (including road cuts) were mapped as pervious surfaces.


·          Compared similar land use signatures as a consistency check.


·          Compared similar IS-valued polygons as a consistency check.


·          IS for all water bodies, including concrete-lined reservoirs, were 0% unless other below-MMU paved or built-up areas existed within the polygon.


·          IS for bridges (1400, 1410, and 1419) passing over vegetation or water were 0%.



Orders of Precedence




2002 Imagery

The 2002 imagery was identical to the 2002 stereo photography; for this reason, no order of precedence needed to be established.


1995/97 Imagery

·          The digital image photography took precedence over the stereo pair photography, even in situations where the stereo pair was dated 1997 and the digital image dated 1995.  The digital image was the ultimate source for the delineations. 


·          When 1995 and 1997 aerial photos or images both coved the same area, the 1997 photos or images took precedence. 


Land Use









Land Cover








LU/LC Change Criteria

A LU/LC change is defined as a physical change in the LU/LC represented by different photo signatures on the 1995/97 and 2002 orthophotos for the same geographical area.   If the area of change conforms to the project mapping criteria, the interpreters delineate new boundaries, as needed, and assign new codes for the 2002 LU/LC data item.  The original polygon boundaries are not deleted and each affected polygon carries both the original 1995/97 LU/LC code and the new 2002 LU/LC class.


Upland Polygons


·          Change in upland polygons was captured, and the resulting polygons were coded appropriately and delineated to match the 2002 imagery.


·          Linework between upland features was not adjusted when a change to either one or both resulted in both units sharing the same LU/LC and IS codes.  This occurred in instances of physical change to the LU/LC feature within unchanging boundaries, and/or actual changes to the dimensions of the LU/LC feature where both polygons ended up carrying the same code structure.  In all other instances between LU/LC features, whether change is involved or not, linework was adjusted to correct registration when needed.   


FWW Wetlands


·          If a FWW polygon underwent a change (including both built-up and non built-up land use), then it was delineated and coded for the appropriate code and IS value.  If the change took place throughout the entire FWW polygon, then the entire polygon was coded as a change.



·          If an FWW polygon underwent a change to a specific non built-up urban or agricultural land use, it was coded as the wetland equivalent of that land use. 


o         If the change resulted in an area of maintained grassy lawn, it was coded as 1750. 


o         If the change resulted in an athletic field, golf course, ball field, or other recreational land use (but not built-up or filled), it was coded as 1850. 


o         If the change resulted in an agricultural land use, it was coded as 2140


o         If a 2140 agricultural wetland was no longer being cultivated and was not built-up, maintained lawn, or a recreational use, then it was coded as 2150 (Former Agricultural Wetland). 


·          If the change involved land cover growth, the FWW code was changed to the new land cover code.  For example, instances where trees grew from emergent or shrub categories, or where coniferous shrubs overgrew deciduous shrubs would be coded with the appropriate land cover value. 


·          A 7430 wetland that changed naturally and significantly was changed to the appropriate wetland vegetation category.


·          If the FWW polygon had changed, and it was considered “negative,” this was manifested in portions of the imagery where a taller order of vegetation was replaced with a shorter order.  If the negative change was in the form of man-made disturbance, such as logging, then the 7430 disturbed wetland code was assigned in 2002. 


·          If the FWW polygon had changed but the change itself was below MMU and unable to be aggregated, then the linework and code were left as is.  However, if the change itself was below MMU but could be potentially combined with an adjacent polygon, then aggregation was attempted.  It could be accomplished by combining the area of change in the FWW polygon with an adjacent polygon that was either FWW or non-FWW.


·          One example is an above-MMU logged area contained for the most part within upland tree polygons, but occasionally moving into adjacent below-MMU sections of wetland polygons.  The below-MMU wetland sections will be delineated and the codes will be changed to the corresponding upland disturbed code for aggregation purposes.


·          Where existing and/or above-resolution bridges crossed over a FWW water body, the resulting intersection was delineated as 1419 and assigned an IS value of zero.  The polygon would not contain a Cowardin item unless supported by history (i.e. the road was widened during the course of the project, reached linear feature MMU, and was then delineated; the resulting polygon crossing over the water feature would in that case contain a Cowardin code).


Tidal Wetlands (Non-Cowardin)

·          Tidal wetland polygons were never restricted by the same constraints applied to the FWW Cowardin wetlands. Preservation of the original polygon boundaries was not required so tidal wetlands were delineated and coded per the general change and retroactive mapping criteria of the project.   


LU/LC Hydrology

The 2002 LU/LC hydrology mapping criteria represented a significant departure from the 1995/97criteria due to the concurrent statewide hydrology mapping effort.  To ensure that the LU/LC water polygons were coincident with the water features captured in the Lakes hydrology coverage the following mapping criteria were established: 


·          All linework was adjusted for polygonal water boundaries to match the 2002 imagery, whether or not change had occurred.  Polygonal water bodies that met the 2002 MMU but were not delineated in the previous update were pulled out and retro-mapped to the 1995/97 dataset.


·          The 2002 imagery reflected drought conditions throughout the state.  Therefore, changes in water body levels were only mapped if the interpreter’s determined the change was not drought related.


Other General Criteria


·          Changes along coastlines, including the shoreline of the Delaware River, that occurred due to erosion or deposition greater than 60 feet were delineated and coded as a change.  Coastal changes usually resulted in LU/LC codes indicating ocean or beach.  For the Delaware River, LU/LC changes were coded with wetland codes consistent with surrounding wetlands. 


·          In general, separate, distinct agricultural fields in the process of being developed were coded as 1700 or 4410 (as appropriate) if not directly under construction.  This situation could often be recognized by new houses built on a former agricultural field where there was an obvious separation between that particular field and similar, undeveloped fields nearby.   The houses indicated that the field had been sold for development; therefore, even if no obvious change to the remaining portions of the field was evident, its land use had changed.  In these instances, a change to the land use directly affected accurate coding of the land cover.


Burned Areas


·          For burned areas where the vegetation remaining was still relatively intact (where the land use could be readily determined), the polygon in which the burned area was included was not coded out as burned. 


·          For upland areas where a severe burn occurred (blackened, tree crowns gone), the area was delineated separately and coded as a change with a LU/LC code of 4500. 


·          For wetland areas where a severe burn occurred (blackened, tree crowns gone), the area was delineated separately and coded as a change with a LU/LC code of 6500. 


Section 5:            Hydrology



NJ DEP contracted AIS to create a statewide hydrology dataset, composed of two GIS coverages, Streams (arcs) and Lakes (polygons).  The hydrology mapping effort was performed simultaneously with the 2002 LU/LC update, using the same digital orthophoto base, hardcopy stereo-paired imagery, and heads-up digitizing techniques. 


The stream arcs were coded for stream type and flow direction.  The water polygon boundaries were captured coincident to the LU/LC layer using the same mapping criteria for the LU/LC water to create a seamless, sliver-free integration between the two datasets.  NJ DEP’s existing hydrology coverage was used to identify previously mapped water features.  Code attributes associated with the existing hydrology were not transferred to the new stream layer.  NJ DEP intends to conflate the codes from the existing hydrology to the new stream layer as a separate project.   


Minimum Mapping Unit

Streams (arcs) = minimum of 10’, less than 30’ in width

Lakes (polygons) = 30’ or greater in width, 1 acre in overall area


Stream (arcs) Classification

1 = Stream

Arc representing visible water that appears as a natural stream course.  This category also includes former ditches that have naturalized and straightened streams (non-ditch). Open water passing under bridges is also captured as a stream.


2 = Proxy-Centerline (PC)

Arc drawn through water polygons to provide continuity with stream arc network for flow modeling purposes.  They do not represent the official centerline of the water body.  Typically, a single PC was mapped through each water feature, excluding side-streams entering into the feature


3 = Artificial Connector (AC)

Arc representing underground passage of stream through a man-made feature such as a culvert.  Artificial connectors are also mapped where they provide connectivity of the stream network in areas where an underground stream connection can be inferred.  Bridges are not considered artificial connectors.


4 = Ditch

Man-made open water features created for the purpose of moving water from one location to another to drain wetlands, prevent flooding, or provide drainage for urban areas. Typically found in wetlands, near roadways, and in urban areas.


5 = Invisible Stream

Arc representing a stream in NJ DEP’s existing hydrology coverage that is not visible on the 2002 imagery, yet the surrounding area appears to support the continued presence of the stream, i.e. undisturbed wetland and/or upland vegetation, no obvious man-made or natural disturbance that would impact the existing stream flow.


Stream (Arcs) Mapping Criteria



Arcs were mapped as close as possible to the visible center of the water.


Proxy Centerline

All stream arcs contained within the boundaries of a water polygon were coded as proxy centerlines (PC).  This includes arcs passing through culverts, dams, and other artificial structures that have been aggregated into the water polygon due to mapping resolution.  


The type of polygonal water feature dictates the position of the proxy-centerline within the water polygon.  


Ÿ         Tidal Water – PC followed deepest part of drainage, if visible and/or distinctive.  Where multiple braiding of streams appears within a single tidal water polygon due to lower tide conditions, the PC follows the deepest channel wherever possible.  If no single channel is followed, the PC will be drawn through the approximate center of the tidal water polygon.


Ÿ         Rivers – PC followed approximate center of river. The PC could be split to show flow around large, mid-stream, islands when the islands meet the LU/LC mmu of one acre.


Ÿ         Lakes – PC was mapped across the length of the lake where an above resolution stream (>10’) entered and/or exited the water feature.  PCs were not captured for lakes, or the “fingers” of lakes, if there was not an above MMU stream ingress/egress.          


Artificial Connector

Artificial connectors were mapped starting at the point where the visible stream disappears from sight underground and ending where the stream remerges into the open.   



Arcs were mapped as close as possible to the visible center of the water. 


Invisible Stream

Ÿ         By definition, invisible streams do not appear as visible water on the 2002 imagery.  These streams are only mapped where there’s a correlating stream on NJ DEP’s existing hydrology coverage and the photo signature supports the continued presence of the stream.

Ÿ         Where possible, the interpreter delineated the stream arc matching it to visible linear wet signatures and stream topography in the approximate location of the original NJ DEP stream delineation.  Where the photo signature is completely homogenous and indistinct, the interpreter maps the position of the invisible stream by correlating it to the existing NJ DEP stream delineation.


Lakes (Polygon) Classification

1 = Streams (Anderson LU/LC 5100)

2 = Natural Lakes (Anderson LU/LC 5200)

3 = Artificial Lakes (Anderson LU/LC 5300)

4 = Tidal (Anderson LU/LC 5410 and 5420)


Lakes (Polygon) Mapping Criteria

Refer to the LU/LC criteria.



Section 6:            Data Dictionary



Land Use

The current LU/LC Anderson classification. 


Impervious Surface.

The current IS percentage. 



4 = LU/LC and/or IS code confirmed during on-site field survey.




Streams (Arcs)

1 = Stream

2 = Proxy Centerline

3 = Artificial Connector

4 = Ditch

5 = Invisible Stream


Lakes (Polygons)

1 = Rivers/Streams (Anderson LU/LC = 5100)

2 = Natural Lakes (Anderson LU/LC = 5200)

3 = Artificial Lakes (Anderson LU/LC = 5300)

4 = Tidal (Anderson LU/LC = 5410 or 5420)