more height maps stuff

How would I go about making a height map for a very huge 3d terrain? I'm making a turn based strategy game on the fur trade, so I need a fairly large environment. I am currently using photoshop to generate the environments, and they turn out being far too small.

Also, do you know if there is a such thing as a resource of gps data for use in heightmaps? The simcity 4 guys seem to have found one... Either that or just a good source for textured heightmaps.

There are several Terrain editors in the work, and some are available. There is one main problem with terrains, you cannot use any size. If you want to have an endless world, you need some kind of Occlusion system, that will only load/create and display the region you are currently walking trough.

It's a nice Idea to use GPS Data to produce heightmaps. Some people from blitzforum.de used to play around with their GPS Data recorders and Blitz, and they had a working converter/interface. I think t isn't that hard if you study the GPS Data format. There will be some infos about the Map position and some infos about eg. Ground height. So it could be translated directly to a heightmap.