Circles are drawn at 1 mile increments from the square. Assuming bicycle speeds of 10 mph and walking speeds of 3 mph, travel times are 6 minutes and 20 minutes per mile
Constructed using the Google Maps API and Jon's Map Tracer Utility.
Another nice example of google maps is USA running maps at http://www.walkjogrun.net/. This site uses google maps to allow you to lay out running routes with mileage and projected times.