once you have the latitude and longitude, you can lookup the corresponding address, for example:
http://maps.googleapis.com/maps/api/geocode/json?latlng=42.5,%20-70.89&sensor=true';
you could use that result to pre-populate the address fields in the address form.
i found an example from a google search search for:
get address from html5 geolocation
http://techslides.com/html5-geolocation-address-form-filler/