A Planisphere of Her Majesty's Martian Colony
This was my entry in the May/June 2011 Light Challenge. Most of the work was done in Inkscape, including the paper texture and other effects. I also used QuantumGIS for tracing out the major landforms and projecting them, gdalwarp to reproject the DEM I used as a basis for the map, The GIMP for various minor tasks like resizing files and adding/removing alpha channels, and some custom programs written in Ruby to generate the graticules and the orbits.
My data sources were a Martian DEM from NASA, and various data (Tilts, radii, orbit eccentricities and other orbital parameters, and the math for the orbit and projection calculations) from Wikipedia, along with photos of Phobos and Deimos. The map is not meant to be an entirely realistic, representation of Mars, even ignoring the canals, reservoirs, cities, and railways, but the locations of major landforms is correct.
The fictional context is that the Victorians have developed an effectively reactionless drive that pushes against the "Luminipherous Ęther" and have used it to colonise Mars, where they are engaged in some form of terraforming project using canals to redirect water. Most of the city names are anachronistic jokes.