The 2002 land use/land cover digital data is provided by watershed management area (WMA).  There area 20 WMA’s in New Jersey.  The statewide land use TYPE change summary was calculated by merging all 20 WMA’s into a combined shapefile and then summarizing the ACRES field by land use TYPE for each of the dates within the datasets.  County-level stats were calculated by converting the merged shapefile to a raster grid on the TYPE field and then tabulating areas by a county shapefile. WMA-level stats were generated by summarizing the ACRES fields by TYPE in the original WMA shapefiles.

It should be noted that the values of Land Use/Land Cover types for 1995 in the newly released dataset (released in 2007) differ somewhat from the 1995 values of the older dataset (released in 2000).  This is attributable to changes in the spatial resolution of the aerial imagery as well as advances in GIS technology and interpretation methodology which have evolved over the three different dates of acquisition: 1986, 1995, and 2002.  Some of the LU/LC polygon boundaries originally mapped in 1995 were subsequently modified in the 2002 LU/LC data set. 

1995 – 2002 Land Use/Land Cover Change

1986-1995 Land Use/Land Cover Change

These types of changes are to be expected with advancing technology.  The important factor is that the old 1995 interpretation was mapped with a similar method to the 1986 interpretation and therefore captured comparable land use changes.  Likewise, the new 1995 interpretation was mapped with a similar methodology of the 2002 interpretation. Thus the quantities of change depicted in each dataset represent the best available information for the change experienced in each time period.

There are multiple approaches that one can take to evaluate Land Use/Land Cover changes in such a GIS database.  This preliminary analysis provides general values of net change by summarizing the “TYPE” category of the dataset which is a generalized classification.

In addition to the general TYPE classes employed in the database there are also more highly detailed land use codes based on the Anderson classification system.  The Anderson classification system differs on certain wetland LU/LC categories.  The general TYPE classification places all delineated wetlands under the WETLANDS label.  The Anderson codes places certain “altered” categories of wetlands into Agriculture, Urban and Bare categories.  An example would be a cranberry field which is considered wetlands under the TYPE label while under the Anderson label is considered agriculture.

This differentiation in wetlands categorization make it possible to have different values of urban, agriculture and barren acreage depending on how the altered wetlands are handled.  Our detailed analysis to be released in later Spring 2007 , addresses this differentiation by separating wetlands into Natural and Altered.  Documentation of this methodology will be released with the final report.