It doesn't snap per se, it just have same hotkey for rotation and selecting next/previous city/unit. Deselect it and you can rotate around the point you see.

I have the same problem. I can't rotate the map at 360°. It's pity because the player cannot enjoy the view of the map through every angles, but it's also a problem for gameplay and especially for battles. For example: it is sometimes possible to access to the top of a mountain plateau through a  very narrow pathway. If this pathway is "behind" the plateau (ie at the north of the hill), the player cannot see it if the map can't rotate at 360°. In consequence, the player potentially losses an opportunity to place its troops advantagely for a battle. So please devs add this feature in the game, just unlock full map rotation.