My recommendation would be that asking for advice in this form is not productive. This is talked about in "Art of the Start". He essentially says that when you present a new idea to people in mass everyone is just going to tell you why it won't work, and that you should ignore all this.

Obviously it is natural and probably helpful on some level to ask people what they think of your idea, but you should be a lot more selective in whose opinion you care about.

While I don't really know anything about this market it sounds like an abstractly interesting idea. But like I said that really isn't important. My suggestion would be to find 3 people you are pretty confident will love this idea (friends of yours on the maps forum) and ask them why it sucks. Then find 3 people who you're pretty sure will hate this idea and ask them why it rocks. Really you just want to pick these people's brains asking very specific questions. Keep doing this until you have refined the idea enough (and have a strong enough grasp of its market potential) that you are ready to take the next step (whatever that may be).

Oh and if this first step takes you more than a week, you're doing it wrong.