Feedback on my web app: Compare Places

I'm looking to get some feedback on a map comparison site I've just built:

http://www.compare-places.com/

In particular I'm interested in your thoughts on the interface:

Is it clear how it works? If not, what didn't make sense? Do you find it easy to use? Any features that you'd like to see added?

At present it doesn't really have a purpose other than as a learning tool. I'd be interested in any thoughts on what people could use it for.

It's just a side project, so I'm not intending to try to make money off it.

At the moment it uses Slinkset to facilitate map sharing. I'd like to streamline this process so it can all be done from the main page.