Morphometric analysis in geographic information systems: applications of free software GRASS and R

Development and interpretation of morphometric maps are important tools in studies related to neotectonics and geomorphology; Geographic Information Systems (GIS) allows speed and precision to this process, but applied methodology will vary according to available tools and degree of knowledge of each researcher about involved software. A methodology to integrate GIS and statistics in morphometric analysis is presented for the most usual morphometric parameters—hypsometry, slope, aspect, swath profiles, lineaments and drainage density, surface roughness, isobase and hydraulic gradient. The GIS used was the Geographic Resources Analysis Support System (GRASS-GIS), an open-source project that offers an integrated environment for raster and vector analysis, image processing and maps/graphics creation. Statistical analysis of parameters can be carried out on R, a system for statistical computation and graphics, through an interface with GRASS that allows raster maps and points files to be treated as variables for analysis. The basic element for deriving morphometric maps is the digital elevation model (DEM). It can be interpolated from scattered points or contours, either in raster or vector format; it is also possible to use DEMs from NASA’s Shuttle Radar Topographic Mission, with 30m of ground resolution for the USA and 90m for other countries. Proposed methodology can be adapted according to necessities and available tools. The use of free and open-source tools guarantees access to everyone, and its increasing popularization opens new development perspectives in this research field. r 2004 Elsevier Ltd. All rights reserved.