Check this MAP
Goto the Radio Locator
Enter the call sign of stations around your area. Also, remember on the AM band the signals travel farther the lower the number on the dial. But it also has to do how many watts and the station's broadcast pattern. Some patterns are directional.
Which means a station could be broadcasting 15 miles from you, but if it is not broadcasting in your direction, you will probably have very bad, spotty reception. However, if you are in the stations signal path, you maybe able to get that station clear as a bell 40 miles out.
Take WBHE 680 AM Newbury/Louisville for example night time pattern..
The southern part of the signal drops out fast, but the signal to the North is a little stronger.
WLW is non-directional which means it's signals pretty much travels uniformily outward.
WLW 700 Cincinnati
Now here is a sample of Reds Radio coverage in San Diego County...