'Set the number of degrees between each longitude grid.
This is an example method that is specific to this projection
class -- it provides a more convenient interface than
set_yticks would.'

def set_latitude_grid(self, degrees):

    grid = np.arange(((-90) + degrees), 90, degrees)
    self.yaxis.set_major_locator(FixedLocator(np.deg2rad(grid)))
    self.yaxis.set_major_formatter(self.ThetaFormatter(degrees))
