I am looking at buying software like Fractal Terrains for the purpose of mapping an entire planet, but in order to be useful for me, it has to be able to do a particular function which is integrate with pre-existing maps.

My understanding is that most of this software is geared toward quickly creating random worlds, which is somewhat the opposite of what I want to do; it's more the planetary mapping, projection, and climate simulation side of things that interests me.

Ideally I'd like to be able to build a planet more naturally, beginning with determining the tectonic plates and so on to calculate location of mountain ranges etc. At the very least, one particular continent has already been mapped out in quite some detail and I would need to be able to integrate that continent, as it currently exists, into a global map.

I just thought I'd check before I go and spend money on some software that it can actually do what I want. The software features lists don't really seem to cover this area for Fractal Terrains, and I am not sure what other software might be out there. I'm particularly interested in getting globe-based mapping software that can automatically handle scale and projection matters for me, as that stuff tends to make my brain hurt!

Thanks in advance.