Geolocation search based on town

We’d like to use geolocation search where the starting point is a town stored in our EM site chosen from the towns dropdown list on the search form. It matching of town to geo coordinates needs to be done in PHP with no interaction from user apart.

How to best find a geo coordinate for a town stored in EM? Retrieving a central point of the town would be ideal. Retrieving the coordinates of any location within the town would also do for the time being since the radius we use covers all nearby towns in either case.

http://wordpress.org/plugins/events-manager/