These files are zipped 10-meter resolution raster images in ERDAS Imagine single-band format. The coordinate system is DE State Plane (NAD 1983 HARN) meters. Cell values range from 0 to 100, indicating square meters (and percentages) of impervious surface in each cell as of early 2007. They can be used with 10-meter resolution digital elevation data to model surface runoff.
These permeability maps were derived from binary 1-meter resolution impervious cover rasters obtained from Mike Mahaffie at the Delaware Office of State Planning Coordination. The source files are available from the Office of State Planning Coordination webiste. The source rasters have three data values: 1=background (outside the county); 2=pervious surface; 3=impervious surface. At 1-meter cell resolution, they are well suited for localized stormwater modeling, but may be cumbersome for large-area analyses: the mosaicked Sussex County file has about 56,000 rows, 59,000 columns, and 3.34 billion cells.
I converted the source layers into 1M-resolution binary rasters
(1=impervious; 0=not). I then set the output raster resolution to 10
and used Arc's Focal Statistics tool to sum the square meters of
impervious surface in each 10x10 cell.
The source data for Sussex County are distributed as two separate
east and west halves of the county. I processed these separately and
mosaicked the final permeability maps to create a single county-wide map.
These data are distributed free of charge without any warranty as to accuracy or correctness.
Please reference this webpage when publishing any analysis based on these data.