Extracting topographic structure from digital elevation data for geographic information-system analysis

TLDR

Software tools at the USGS EROS Data Center extract topographic structure and delineate watersheds and flow paths from digital elevation models. The tools, implemented as special‑purpose FORTRAN programs linked to raster and vector analysis and database packages, first generate conditioned data sets—filled DEM, flow direction, and flow accumulation—before producing drainage networks, overland paths, watersheds, sub‑watersheds, or pour‑point linkages. Computer‑generated drainage lines, watershed polygons, and pour‑point linkages can be transferred to vector GIS, and their close agreement with manually delineated features demonstrates that the tools save analyst time.

Abstract

Software tools have been developed at the U.S. Geological Survey's EROS Data Center to extract topographic structure and to delineate watersheds and overland flow paths from digital elevation models. The tools are special purpose FORTRAN programs interfaced with general-purpose raster and vector spatial analysis and relational data base management packages. The first phase of analysis is a conditioning phase that generates three data sets: the original DEM with depressions filled, a data set indicating the flow direction for each cell, and a flow accumulation data set in which each cell receives a value equal to the number of cells that drain to it. The original DEM and these three derivative data sets can then be processed in a variety of ways to optionally delineate drainage networks, overland paths, watersheds for user-specified locations, sub-watersheds for the major tributaries of a drainage network, or pour point linkages between watersheds. The computer-generated drainage lines and watershed polygons and the pour point linkage information can be transferred to vector-based geographic information systems for further analysis. Comparisons between these computer generated features and their manually delineated counterparts generally show close agreement, indicating that these software tools will save analyst time spent in manual interpretation and digitizing.