Well I guess what is your definition by reliable. For example, the process that I wrote, providing the zip code I live in and the zip code of a neighboring town would return 7 miles, however, Mapquest would return 10.0 miles. Here is the problem: MapQuest calculations work against GeoSpacial data (roads, interstates, etc) my process applied a Great circle theory to an origin latitude and longitude against a destination latitude and longitude resulting in a straight line. Since the shortest distance between 2 points is a straight line my calculations are obviously going to return a shorter distance than that returned from a Mapping service that takes into account all things one might deal with when they travel.
So how reliable do you need this?
Read this if you want to know how to get a correct reply for your question:
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