Gets the user enter max and min values of where the 
        raster points should appear on the y-axis

        :returns: (float, float) -- (min, max) y-values to bound the raster plot by

def values(self):
        """Gets the user enter max and min values of where the 
        raster points should appear on the y-axis

        :returns: (float, float) -- (min, max) y-values to bound the raster plot by
        """
        lower = float(self.lowerSpnbx.value())
        upper = float(self.upperSpnbx.value())
        return (lower, upper)