Start a new game in the "Legends" mode. This allows you to export a multitude of detailed information about the world, among them detailed maps using the [d] key. The options "Elevations including lake and ocean floors" and "Elevations respecting water level" both produce heightmaps of the world while the other options allow you to export a texture to match it.
The graphics are exported into the base Dwarf Fortress directory (the same one where DwarfFortress.exe
resides), under the names ...
world_graphic-el-
region name-
some numbers.bmp
for the "elevation including lake and ocean floors" mapworld_graphic-elw-
region name-
some numbers.bmp
for the "elevation respecting water level" map
For the highest size region (257x257), they are 4112x4112px in size. They look like this, scaled down (in order: with lake/ocean floors, with water level):