title: Finding the center point of a city
body: <p>We are purchasing a database of zip codes and their corresponding Lat/Long.  I want to store cities in a separate table with a lat/long point representing the center of the city.  Can I calculate that based on taking all of the zips that belong to that city, getting the min/max points for each direction, and taking the center point of the resulting rectangle?</p>
  
  <p>Is there a more accurate method?  I want to avoid purchasing another DB.  We haven't purchased the full DB yet so I can't just try it and compare the results to Google Maps.</p>