Unfortunately that kind of use case is something that can be accomplished in conjunction with another service, such as beacons or geo-location using Gimbal.
In order to be able to meet this kind of use case, the device would have to be uploading it's location data constantly, which as you can imagine, might drain the users battery life pretty quickly! So, we want to prevent that as much as possible.
Urban Airship provides historical location for customers on a paid plan, which would allow you to send a push to users who have been in a particular location in x time frame.
With Gimbal, however, you get the option to message users if they enter or exit a particular geofence. So, in essence, you could message all users in a particular region should they cross a geofence.
Right now, though, it sounds like historical location might be your best option right now, however keep in mind that the minimum amount of time you would be able to query for historical location would be about 6 weeks.
Your only other option is to set tags based on where that user is at the moment, and send to the tags themselves. They will not be as real-time as the other options, but would get you closer to your use case.