def user_loc_value_to_instance_string(axis_tag, user_loc):
    """Return the Glyphs UI string (from the instance dropdown) that is
    closest to the provided user location.

    >>> user_loc_value_to_instance_string('wght', 430)
    'Normal'
    >>> user_loc_value_to_instance_string('wdth', 150)
    'Extra Expanded'
    """
    codes = {}
    if axis_tag == "wght":
        codes = WEIGHT_CODES
    elif axis_tag == "wdth":
        codes = WIDTH_CODES
    else:
        raise NotImplementedError
    class_ = user_loc_value_to_class(axis_tag, user_loc)
    return min(
        sorted((code, class_) for code, class_ in codes.items() if code is not None),
        key=lambda item: abs(item[1] - class_),
    )[0]