Coordinates

Using a google map you can allow your users to set locations by simply dragging a marker on the map.

Latitude:    Longitude:

Drag the marker on the map to set the coordinates:

 

Two fields - one for longitue and one for latitude - are updated as the marker is dragged on the map. These fields could be hidden as well. Putting them into a form and adding a submit button is all you need to allow users to update locations.

The javascript code for this can be found here