To be usefully terraformed, the atmosphere would have to have a surface pressure pretty close to our own. I'd say at least 450-600 millibars. Lets go with 500mb, about half an atmosphere. Surface pressure is the weight of atmosphere above a given area of the surface. With Mars having about a third of Earth's gravity this requires about three times as much mass of air for the same pressure. So for our example, this would be about 1.5 times as much air as Earth, with a commensurate increase in optical density. I'd expect a terraformed Mars to be a good deal hazier than Earth actually. Also clouds would tend to build up a lot higher, making them appear very opaque. A somewhat dry Mars wouldn't have thin clouds so much as infrequent clouds. That seems to be what someguy's image shows.

btw, The large optical thickness is beneficial for terraforming Mars as it also means the greenhouse effect will be large, warming the planet up.

All that hidden surface doesn't make a great map, but it is a good view of the planet from space. Sometimes in a space game you need a good planet map, sometimes you just need to know what you see out the cockpit window...