This is an idea I've had for the ultimate civgame for a long time that handles the multimap problem quite differently. First off you start in the prehistoric era in a map that actually is a small area of the world map as seen through a microscope. Then when you reach enough technological sophistication this map is converted to a normal world map. This idea can be extended further, so when we reach a certain stage we no longer care about individual cities on earth but the earth itself is handled like a city. And depending on how much infrastructure you've built up determines what kind of "buildings" are on it. And later when the solar system is sufficiently developed the map transforms again into a galactic map where each habitable solar system is handled like it's own city. At any given time you have no more than one or two maps to care about.