General Comments, New Jersey 2002 Land Use/Land Cover Update Project
The 2002 updated land use/land cover (LU/LC), and impervious surface (IS) layer was mapped for the purpose of providing trend analysis data throughout the state. A major component of this update was to accurately delineate water body features and improve related Hydrography data layers statewide. Aerial Information Systems, Inc., (AIS), Redlands, CA. performed all work, under the direction of the New Jersey Department of Environmental Protection (NJDEP).
This is the third iteration of the land use/land cover data NJDEP has produced. The 2002 CIR digital imagery was used as the base imagery for this update. Due to significant improvements and quality of this imagery, the compilation of the 2002 LU/LC update was conducted on a more detailed level than the 1995/97 LU/LC. The restrictions which were in place in the previous effort, to maintain the 1986 data codes and Freshwater Wetlands (FWW) lines, has been relaxed. Early on in the project, it became apparent that to accurately delineate the hydrologic features, the 1986 polygon boundaries and codes needed to be removed for this update. Only the FWW - COWARDIN and CLASS fields are carried forward from the 1986 data layer when appropriate. Therefore, as a starting point for this update, the 1986 - 1995/97 data layer was dissolved on the LU95, IS95, COWARDIN and CLASS fields codes.
The user needs to be aware of these differences and their significance while using the 2002 LU/LC layer as a trend analysis tool. Trend analysis studies rely upon the comparison of data from one year to another in order to identify areas of change. Under ideal circumstances, all of the data sets have been generated using the same classification, minimum mapping unit (mmu), input scale, mapping method, and mapping medium and it’s only the year of the photography that is different. Therefore, when the update is completed, the user only needs to compare the original data to the updated data set and look for new or different polygon boundaries and/or codes to identify areas of change, without having changes due primarily to different mapping methodologies affect the analyses.
To eliminate the need for users to independently compare 1995/97 and 2002 data sets, this update was produced by adding appropriate polygon boundaries and land use codes defining LU/LC in 2002 directly to the 1995/97 base data layer. Where change is evident new line-work was added along with new LU02-codes and IS02 values to describe the 2002 conditions. The LU/LC as interpreted from the 1995/97 imagery are defined in the 1995 land use attribute fields. The 1995/97 codes (LU95 and IS95) were changed in this update if, the photo interpreter determined that, a previous code was in error or a new adopted code was more descriptive. This correcting and/or "retro coding" of the 1995/97 codes was applied across the state with one exception. The Coastal Wetlands - Saline Marshes code 6110 was not modified with the addition of the 6111 and 6112 codes. These polygons are also considered not a change and therefore not identified as such in the CHANGE attribute field.
Users simply need to compare the 1995/97 and 2002 polygon boundaries and LU/LC codes in this one updated layer to examine land use change in any area. The 1995/97 data in this update are considered "Revised". Total acreage by Level 1-land use categories will be different for the two versions of the 1995/97 data. In addition to the reasons requiring retro coding, the focus on improving the Hydrography data layers resulted in changes in the category totals. Users interested in the 1986 data must obtain the codes from previous update for comparison.
The basic process for completing the update was to examine the 1995/97 base data layer over the 2002 digital imagery and add the appropriate line work and codes to define the 2002 landscape. NJ DEP provided the baseline LU/LC layer from their GIS database. The polygonal hydrography data and the River/Stream network, including water body proxy-centerlines, were produced as part of the land use update.
Assigning new COWARDIN classifications was beyond the scope of this present mapping effort. The COWARDIN and CLASS fields in the attribute table for the LU/LC update layers are legacy attributes from the FWW data set used to create the baseline 1986-1995/97 LU/LC layer. The COWARDIN and CLASS fields in the attribute table for the LU/LC update layers were not updated if the wetland polygon has undergone a change. The COWARDIN and CLASS values can be applied to the polygon only if it has not changed since 1986. Changes to the COWARDIN and CLASS values would have to be determined on a case by case basis and only to adjacent areas of identical landuse.
In order for the final layer to be used to accurately analyze the 1995/97 to 2002 land use changes, modifications to the layers were undertaken during the update process to reduce the effects of having different mapping methodologies used in the 1986 and 1995/97 projects. Mis-alignment of the baseline data to the digital image was predominantly caused by the differences between the 1986 basemap, the 1995/97 orthophoto digital image and the 2002 orthophoto digital image creation process. The 1986 photo base maps were created as individual maps based on the USGS topoquad corner tics. The 1995/97 digital imagery was created using a sophisticated, integrated, aero-triangulation method, as a standard USGS. The 2002 was created using Digital orthophotography, a process which converts aerial photography from an original photo negative to a digital product that has been positionally corrected for camera lens distortion, vertical displacement and variations in aircraft altitude and orientation. The imagery was captured at a negative scale of 1" = 1600' in the spring of 2002. The ortho-rectification process has achieved a +/-4.0 ft. horizontal accuracy at a 95% confidence level, National Standard for Spatial Data Accuracy (NSSDA).
Since the mis-aligned polygons may lead to incorrect land use change analysis, many of the polygon boundaries were adjusted to fit the more accurate 2002 imagery during the delineating and coding land use changes. Contractually, AIS was responsible for only correcting the registration of non-change polygons off more than 30 feet. In actuality, AIS corrected the registration of many non-change polygons excepting Cowardin wetlands. NJDEP, during the review process, corrected as many as possible and made determinations on sliver polygons containing Cowardin codes as to whether the sliver is a result of mis-alignment. Sliver polygons where either merged with adjacent land use of regardless of a Cowardin wetland code, conversely, sliver polygons may have been merged with adjacent wetland polygons if the imagery and interpretation of supporting data layers justified it.
The minimum mapping unit (mmu) of 1 acre has not changed for this update. Many of the problems inherited from the 1986-update, misalignment, imagery resolution and a 2.5 acre mmu are being corrected. With each update the LU/LC class delineation will improve to match new imagery and will likely be modified to meet the needs of the department.
NJDEP has adopted a watershed based management approach, so the data production was completed by watershed management area (WMA). These WMA’s are based on hydrologic drainage boundaries (HUC8, HUC11 and HUC14) developed by the USGS and edited in 2000. There are 20 WMA’s covering the landmass of the state. Migrating to the WMA as the production boundary modified the area statistics reported for several WMA's.
The final data layers were delivered to NJDEP as ArcInfo coverages. These data layers were imported into a SDE geodatabase for QA/QC review. Editing of the data by NJDEP was conducted in this environment with topology. Drafts were appended to the existing feature class and edge-matched.
ADDITIONAL REFERENCE DOCUMENTS
The following documents contain additional information concerning the LU/LC update project. Users of the data should review all documents before using the LU/LC update layers in any analyses.
UPDATE2002.HTML Detailed discussion of the 2002 LU/LC update project
CODELIST2002.HTML Land use codes used in the New Jersey LU/LC 2002 Update mapping project
ANDERSON2002.HTML Land use/land cover 4-digit code descriptions for the 2002 Update
The following are documents relating to the 1995/97 LU/LC project and provide in detail the methodology used at the time and history of codes.
UPDATE.HTML Detailed discussion of the 1995/97 LU/LC update project
CODELIST.HTML Land use codes used in the New Jersey LU/LC Update mapping project
ANDERSON.HTML Land use/land cover 4-digit code descriptions
ITUM.HTML Description of the ITUM methodology
FWWINTEG.HTML Description of process used to integrate FWW data sets in the ITUM
FWW.HTML Wetlands Cowardin alphanumeric classification system.