Example using precision from geokit gem to ensure geocoding is sane

some_model.rb

class SomeModel < ActiveRecord::Base
  validate :geocode_address
  
  def address
    [street_address, city, state, zip].select{|a| !a.blank?}.join(', ')
  end
  
  
  # ...
  
  protected

    def geocode_address
      return true unless new_record? || street_address_changed? || city_changed? || state_changed? || zip_changed?
      return true if address.blank?
      
      geo = Geokit::Geocoders::MultiGeocoder.geocode(address)
      if geo.success && geo.accuracy.to_i > 3 # Ensure better than county-level precision (http://code.google.com/apis/maps/documentation/geocoding/v2/index.html#GeocodingAccuracy)
        self.latitude, self.longitude = geo.lat, geo.lng
        self.street_address, self.city, self.state, self.zip = geo.street_address, geo.city, geo.state, geo.zip
      else
        errors.add_to_base("Unable to geocode address -- please be sure you entered it correctly")
      end
    end
end