def valid_coordinates(marker):
    """Checks wether coordinates are valid: a number between 90 and -90 for latitude and -180 and 180 for longitude

    :param marker:
    :type marker: dict[str, str]
    :return:
    :rtype: bool
    """
    try:
        if abs(float(marker['long'])) > 180 or abs(float(marker['lat'])) > 90:
            raise ValueError
    except (KeyError, ValueError):
        return False

    return True