When you open Poke Radar you'll see that lots of Pokemon have already been located in your area (some places have more and others less). Click on any Pokemon to see the name of the trainer as well as the date on which the Pokemon was captured.
Another really interesting feature in Poke Radar lets you search for a specific Pokemon. Just click the magnifying glass icon, choose the Pokemon you're interested in, and wait a few seconds. Then the app will show the Pokemon of that specific type that are closest to you. Sometimes you'll find they're five blocks away – and other times, in the next city over.
Poke Radar is a very useful app for Pokemon trainers. That being said, be careful in the more dangerous parts of your city – especially if a Mew and a Mewtwo show up in those areas.