Abstract: MAPCHAT is a system for on-line capture and dissemination of tactical and terrain information among geographically separated users. It has a distributed, multi-server, multi-client architecture that enables the users to capture and communicate spatial and non-spatial data, in the form of overlays, to other users in the LAN, or WAN, or to mobile users in field locations, connected through a wireless interface. The MAPCHAT system consists of Windows PCs, loaded with MAPCHAT software, and a back-end repository of maps and overlays (Windows PC with Oracle Database Server), all connected via a LAN, WAN or wirelessly using GPS-fitted receivers for mobile subscribers. MAPCHAT works on the principle of normal Chat software with one significant difference: in addition to the textual chat messages, it handles geographic data encoded as textual data in XML format. MAPCHAT software consists of two components—the server and the client. The server component is a normal Chat server implemented using TCP/IP socket programming in Java2. The MAPCHAT client is a powerful GIS tool, capable of display and analysis of geographic data in various formats, with an added XML parser and a communication module.