def getTZLookup(tzfname='cities15000.txt'):
    """Returns a mapping from gps locations to time-zone names.
    The `tzfname` file is read to map gps locations to timezone names.
    This is from: http://download.geonames.org/export/dump/cities15000.zip
    Returns a list of `((lat, lon), timezone)` pairs.
    """
    ret = [l.rstrip('\n').split('\t') for l in open(tzfname) if l.strip()]
    ret = [((float(l[4]), float(l[5])), l[17]) for l in ret]
    return ret