I think Terragen would be very appropriate for some parts of your project, specifically the visualization of particular regions and parts of your world.
Terragen is not the best thing for creating "maps", i.e. depictions that focus on geographic regions and features, rather than realistic depictions of a place. I'm not sure what might be best for that other than a simple paint or photo editing program like Photoshop. Perhaps Fractal Terrains from ProFantasy?
https://secure.profantasy.com/products/ft.aspFor city maps, buildings, interiors, etc. you would be better off using a dedicated modeling program, or just buying (or downloading free) models that are already built and match the general look and shape(s) you want. You could then import these into Terragen to create your realistic renderings of the scenes, along with character models, etc. if you want.
The scale and difficulty of this project depends a lot on just how customized and specific you want it to be. If you have an exact look in mind for every element of your world, it will take a ton of time and effort to effectively create it digitally. Terragen could form one important part of that process, but would probably be an "end point" rather than a starting point or generator, by which I mean that you would probably want to use a dedicated terrain editor or map making application to start, then output a terrain that Terragen could use, and likewise use a 3D modeling program like Blender or Sketchup or Modo or something for buildings and possibly characters (or Daz for characters), then export the models to Terragen for rendering.
I hope that gives you some idea for a start...
- Oshyan
