'Transforms the ``value`` from plot to data coordinates along the axis ``axis_id``.
This function always ignores zoom. If you need to account for zooming, use :meth:`map_from_graph`.'

def inv_transform(self, axis_id, value):

    if (axis_id in XAxes):
        size = self.graph_area.width()
        margin = self.graph_area.left()
    else:
        size = self.graph_area.height()
        margin = self.graph_area.top()
    (m, M) = self.bounds_for_axis(axis_id)
    if ((m is not None) and (M is not None)):
        return (m + (((value - margin) / size) * (M - m)))
    else:
        return 0
