def _metadata_url(obs_point):
    """ construct a url for retrieving gsv metadata 
        at obs point location"""
    lat = obs_point.geometry.y
    lng = obs_point.geometry.x
    base = 'https://maps.googleapis.com/maps/api/streetview/metadata?'
    latlng = 'location={},{}'.format(lat, lng)
    source = 'source=outdoor'
    url = '{}&{}&{}'.format(base, latlng, source)
    return url
