"Geographic information system"
See "Geographic mapping the Tcl way".
CL has lots of toy maps (of US states, Norway, the Volga River, ...) written as Tcl programs, with "live" canvases, ... He's trying to figure out how to package them so others can see them. A hint of what's possible appears in "Open Cartography" [L1 ].
GRASS [L2 ] is an open-source GIS application that relies on Tk for its GUI.
http://www.mapit.de/index.en.html
http://freegis.org/index.en.html
AM Here is a page devoted to Raster operations on the canvas that bears relation to GIS....