How close do I need to be to the city centre?

Here in Berlin they reach all the way to the city limit. This morning, while driving from my suburb flat to my edge-of-town workplace, I caught three Kangaskhan and three Unown.

They seem to spawn in a big radious. Even in areas that are not longer the city, but close to it. Seem to be more common in big parks as well, although they spawn all over the place