How to obtain longitude and latitude for a street address programmatically (and legally)

Solution 1:

The term you're looking for is geocoding and yes Google does provide this service.

• New V3 API: http://code.google.com/apis/maps/documentation/geocoding/

• Old V2 API: http://code.google.com/apis/maps/documentation/services.html#Geocoding

Solution 2:

In addition to the aforementioned Google geocoding web service, there is also a competing service provided by Yahoo. In a recent project where geocoding is done with user interaction, I included support for both. The reason is I have found that, especially outside the U.S., their handling of more obscure locations varies widely. Sometimes Google will have the best answer, sometimes Yahoo.

One gotcha to be aware of: if Google really thinks they don't know where your place is, they will return a 602 error indicating failure. Yahoo, on the other hand, if it can peel out a city/province/state/etc out of your bad address, will return the location of the center of that town. So you do have to pay attention to the results you get to see if they are really what you want. There are ancillary fields in some results that tell you about this: Yahoo calls this field "precision" and Google calls it "accuracy".