Watch your mini-map before and after stonehenge. When you start out, your capitol is centered in the mini-map, and it zooms out as necessary to contain the explored territory. After you get stonehenge, the mini-map zooms out completely and you see where your civilization is in relation to the rest of the world. This is particularly useful on island and continent maps, because you know where your island is and can more easily guess in what direction to start exploring for other islands.