import math


def get_data_file(lon, lat):
    """
    Returns the correct HGT data file to get elevation from.
    Credit: Aatish Neupane
    Link: https://librenepal.com/article/reading-srtm-data-with-python/
    :param lat: The latitude of the desired point.
    :param lon: The longitude of the desired point.
    :return: The name of the data file.
    :raise: ValueError: If lat/lon are not within supported bounds.
    """

    if 48 <= math.floor(lat) < 60 and 110 < math.floor(lon) <= 121:
        return "N{}W{}.hgt".format(math.floor(lat), math.floor(lon))
    else:
        raise ValueError("Point does not fall within supported bounds")