With the hex-based tiles it should be possible to perfectly tile your cities so that all tiles are being exploited but none are being overlapped, unless they decide to do something really strange with the radius shape. (Possible conflicts with unbuildable terrain aside of course.)
How? The city's area of influence starts small and then grows wider. If you space them out at first, other civs will build in between before the area of influence grows. If you put them close together, when they grow, their influence will overlap (wasteful). Seems like exactly the same situation to me.