You could let users enter their a city and fetch the data locally via javascript. That way, the usage counts against their IP's API limit, not yours.

Edit: To be more clear, this would only work for showing the data to the user that requests it, not sending it back to the server for other users to see.

Yes, except then you're relying on data coming from untrusted users. How long do you think it would take before someone figures out a way to put themselves at the top of the list? ;)

Edit: OK. Assuming you're only looking at data locally, you'll probably run into API limits. Users are only allowed to make 60 requests to the API per minute. My guess is you need more than that to generate these statistics.

Get in touch with the GitHub people. They are some of the most reasonable people on the planet. I'm sure they'll help you somehow.

Totally, that would be cool.

I'd love to see Chicago up there if you get around those limits.

Chicago def should be on it. I'll add it next.

You have Houston but not Dallas? Actually, it would be better if it were by metro if you're not going to let the users choose their suburbs and what not.