As far as I can see there seem to be only three maps, relatively flat, rough and steep. Very limited and boring after only a few games !!!

Is there any way to edit or make new maps ???

There are 3 terrain types to the maps. There are something like 64,000+ maps, each of which is generally within one of those terrain types. Each map is unique, saved to those coordinates. This is deliberate so that the same location (coordinates) can be played again using different mission set ups, a different sponsor, etc. Trade good locations (or tough ones) with your friends!

The three major terrain types mainly have to do with how many levels of terrain, and how many compartments that terrain is broken into by non-drivable features. For example, some proportion of "Relatively Flat" terrain (my guess from many playthrus - about 40%) contains 1 or 2 plateau areas, unreachable except by tunnel, ramp, or flying, but all at the same level above the lowest. Rough and Steep - more terrain isolated bits requiring engineering to get to, and at multiple, and higher levels.

"Maps" are also differentiated by the likelihood of the 4 types of disasters, each of which can occur in 4 levels of frequency/intensity. They are also differentiated by the amounts of the 3 major planetary resources, metals/rare metals, surface sulphur regolith deposits suitable for quickly converting to "concrete", and water.

Also, unrelated to your complaint, but still about maps and terrain: the general map elevation shown when you pick your spot on the globe HAS NOTHING TO DO WITH WIND TURBINE EFFICIENCY! Wind turbine bonuses are determined solely by the altitude of the bit of terrain it is built on, RELATIVE TO THE REST OF THE GRID MAP. Trust me - I've tested this with turbines built on top of Olympus Mons and with turbines built tin the bottom of the Great Rift.