def bounding_box_center(listings)
    maxlat, maxlon, minlat, minlon = -Float::MAX, -Float::MAX, Float::MAX, Float::MAX
    listings.each do |listing|
      maxlat = listing.lat if listing.lat > maxlat
      minlat = listing.lat if listing.lat < minlat
      maxlon = listing.lon if listing.lon > maxlon
      minlon = listing.lon if listing.lon < minlon
    end
   return [(maxlat + minlat)/2,(maxlon + minlon)/2]
  end