Abstract : The Geographic Resources Analysis Support System (GRASS) is a geographic information and image-processing system originally designed to serve land managers and environmental planners at Army installations. GRASS is an integrated set of programs that provide digitizing, image processing, map production, and geographic information system capabilities to its users. GRASS is written in C and is ported to computers running the UNIX operating system. Since its initial development, GRASS has been developed for many applications on a number of different hardware configurations. GRASS Version 4.0 includes significant additions and modifications to system libraries and programming code. This manual contains a program-by-program description of each program's capabilities and uses; a summary of command-line options; and lists of associated or related programs. GRASS, geographic information, image processing, user manuals, Geographic Resources Analysis Support System.