The original USGS DEM data (Mt. Kineo and Woodstock quadrangles) were merged and projected into UTM Zone 19. The resultant grid was clipped to a box surrounding the USDA Forest Service, Hubbard Brook Experimental Forest.
Level 1 DEM: Level 1 DEMs are acquired photogrammetrically by manual profiling or image correlation techniques from either the National Aerial Photography Program (NAPP) or equivalent source photographs. Level 1 30-minute DEMs may be derived or resampled from Level 1 7.5- minute DEMs.
Level 2 DEM: Level 2 DEMs are produced by converting 1:24,000-scale and 1:100,000-scale hypsography digital line graph (DLG) data into DEM format or the DEMs can be generated from vector data derived from scanned raster files of USGS 1:24.000-scale or 1:100,000-scale map series contour separates.
Level 3 DEM: Level 3 DEMs are created from DLG data that has been vertically integrated with all categories of hypsography, hydrography, ridge line, break line, drain files and all vertical and horizontal control networks. The production of Level 3 DEMs requires a system of logic incorporated into the software interpolation algorithms that clearly differentiates and correctly interpolates between the various types of terrain, data densities and data distribution. Water body editing: DEM surface areas corresponding to water bodies are flattened and assigned either map specified or estimated surface elevations. Water body areas are defined as ponds, lakes, and reservoirs that exceed 0.5 inches at map scale and double line drainage that exceeds 0.25 inches at map scale. Water body shorelines are derived from either a hypsographic DLG or by interactive delineation from a 1:24,000- or 1:100,000-scale USGS map series. DEMs are verified for physical format and logical consistency.
Much of the USDA Forest Service data are compiled, processed, and maintained with ARC/INFO software developed by the Environmental Systems Research Institute (ESRI). Much of the information presented uses conventions and terms popularized by ARC/INFO and its user community. The mention of commercial firms or products is for clarity and identification of procedures and methods only, and no endorsements are implied by the USDA Forest Service.