def METHOD_NAME(self, screen_val):
    """map_data(screen_val) -> data_val
    Overrides AbstractMapper. Maps values from screen space into data space.
    """
    self._compute_scale()
    if self._null_screen_range:
        return array([self.range.low])
    elif self._null_data_range:
        return array([self.range.low])
    else:
        return (screen_val - self.low_pos) / self._scale + self.range.low