code: def dist_to_deg(self, distance, latitude):
          
          #   d * (180 / pi) / earthRadius   ==> degrees longitude
          #   (degrees longitude) / cos(latitude)  ==> degrees latitude
          lat = latitude if latitude >= 0 else -1 * latitude
          rad2deg = 180 / pi
          earthRadius = 6378160.0
          latitudeCorrection = 0.5 * (1 + cos(lat * pi / 180))
          return (distance / (earthRadius * latitudeCorrection) * rad2deg)
docs: distance = distance in meters
          latitude = latitude in degrees
  
          at the equator, the distance of one degree is equal in latitude and longitude.
          at higher latitudes, a degree longitude is shorter in length, proportional to cos(latitude)
          http://en.wikipedia.org/wiki/Decimal_degrees
  
          This function is part of a distance filter where the database 'distance' is in degrees.
          There's no good single-valued answer to this problem.
          The distance/ degree is quite constant N/S around the earth (latitude),
          but varies over a huge range E/W (longitude).
  
          Split the difference: I'm going to average the the degrees latitude and degrees longitude
          corresponding to the given distance. At high latitudes, this will be too short N/S
          and too long E/W. It splits the errors between the two axes.
  
          Errors are < 25 percent for latitudes < 60 degrees N/S.