• 10-meter resolution DEM's by county; DE State Plane NAD 1983 HARN (meters); floating-point elevation (Z) values in meters. These are very large files, stored as ArcGIS v.10 layer packages.
• 30-meter resolution DEM's by 7.5-minute quad; UTM-18N NAD 1983 (meters); integer elevations in feet. These are stored in ASCII format, served from a clickable map, and importable to ArcMap.
• 30-meter resolution DEM's by county; both UTM-18N and DE State Plane (NAD83); integer elevations in feet. These are stored in zipped ASCII format and importable to ArcMap. This page also serves "filled" county-wide DEM's that support hydrologic modeling.

The early development of these DEM's was conducted using GRASS; subsequent development has been done with ArcGIS. There are several older pages on this website explaining:

• the creation of the original 30-meter DEMS for Delaware from source hypsography files (1996)
• some basic derivatives (slope, aspect and hillshade)
• some basic hydrologic analyses

A more detailed illustration of hydrologic analysis using ArcGIS is available here.