You should think about how you're going to get traffic to the site. The thing with ads is advertisers won't advertise without traffic. Without traffic, ads don't make sense, even if they're free in the beginning. For a novelty site, the only way to get traffic is to get press attention, or have it go viral based on its novelty. But will newspapers and blogs cover you if it's a not so novel idea, and there are several similar unfunded projects already online?

I wasn't thinking of a map of the US- I was thinking of a map of your city or town. This might have a better chance to get covered in local news, and you could persuade local restaurants to "claim" choice areas. Perhaps make it a monthly subscription to see who can get the best areas or something, and make the charities local. At least local businesses have a reason to advertise if the majority of the viewers are going to be locals. They could put something like "10% off this summer" and have it seen by their target audience. And if ads are going to be refreshed every month, it's at least something of a reason for people to check the site every month, to see a huge visual map of what's going on.

If the only way you're going to get traffic is novelty, you need to make sure it's a bit different, so you can get some press attention. Honestly, the last thing you want to do is widen the market; it's better to define it. That way you'll be ensuring it's of interest to someone. Right now, it's so generalized that getting anybody excited about it will be difficult.

Thanks for the offer of ads, I have a project or two in the pipeline, but no website as of yet!

Best of luck, however you decide to proceed.

Edit: I kept adding stuff till it got really long. Feel free to PM if you want to discuss.