Fractal's just a randomly generated map. I haven't played it, but Earth 18 is just a map of the Earth with 18 civs on it. I think its just for the basic civ and not for BTS unless you download another one.
Earth18's fun; there's a lot of different playstyles on one map. Europe has awesome land - resources every other tile - but six civs on a postage stamp. Asia is a lot like a normal game of Civ. Africa is almost empty - Mali and Egypt only - but short on good resources, with hammerless start spots. Colonization is doable, as South America east of the Andes is uninhabited; in a German game I got some amusement out of chopping down the entire Amazon and carpeting the area with cities.