def union(inputtiles, parsenames):
    """
    Returns the unioned shape of a steeam of [<x>, <y>, <z>] tiles in GeoJSON.
    """
    try:
        inputtiles = click.open_file(inputtiles).readlines()
    except IOError:
        inputtiles = [inputtiles]
    unioned = uniontiles.union(inputtiles, parsenames)
    for u in unioned:
        click.echo(json.dumps(u))