def get_locations(df):
    """
    Get the list of all locations present in the data source.

    Parameters
    ----------
    df : `~pandas.core.frame.DataFrame`
        Astropy data table containing the navostats data

    Returns
    -------
    list of str
        Sorted unique location values present in the data.
    """
    dfg = df.groupby(['location'])
    locations = list(dfg.groups)
    locations.sort()
    return locations