code: def haversine_distance(latitude_1, longitude_1, latitude_2, longitude_2):
      
      d_lat = to_rad(latitude_1 - latitude_2)
      d_lon = to_rad(longitude_1 - longitude_2)
      lat1 = to_rad(latitude_1)
      lat2 = to_rad(latitude_2)
  
      #pylint: disable=invalid-name
      a = math.sin(d_lat/2) * math.sin(d_lat/2) + \
          math.sin(d_lon/2) * math.sin(d_lon/2) * math.cos(lat1) * math.cos(lat2)
      c = 2 * math.atan2(math.sqrt(a), math.sqrt(1-a))
      d = EARTH_RADIUS * c
  
      return d
docs: Haversine distance between two points, expressed in meters.
      Implemented from http://www.movable-type.co.uk/scripts/latlong.html