def plot_phi(self, colorbar=True, cb_orientation='vertical',
                 cb_label='$g_\phi$, m s$^{-2}$', ax=None, show=True,
                 fname=None, **kwargs):
        """
        Plot the phi component of the gravity field.

        Usage
        -----
        x.plot_phi([tick_interval, xlabel, ylabel, ax, colorbar,
                    cb_orientation, cb_label, show, fname, **kwargs])

        Parameters
        ----------
        tick_interval : list or tuple, optional, default = [30, 30]
            Intervals to use when plotting the x and y ticks. If set to None,
            ticks will not be plotted.
        xlabel : str, optional, default = 'longitude'
            Label for the longitude axis.
        ylabel : str, optional, default = 'latitude'
            Label for the latitude axis.
        ax : matplotlib axes object, optional, default = None
            A single matplotlib axes object where the plot will appear.
        colorbar : bool, optional, default = True
            If True, plot a colorbar.
        cb_orientation : str, optional, default = 'vertical'
            Orientation of the colorbar: either 'vertical' or 'horizontal'.
        cb_label : str, optional, default = '$g_\phi$, m s$^{-2}$'
            Text label for the colorbar.
        show : bool, optional, default = True
            If True, plot the image to the screen.
        fname : str, optional, default = None
            If present, and if axes is not specified, save the image to the
            specified file.
        kwargs : optional
            Keyword arguements that will be sent to the SHGrid.plot()
            and plt.imshow() methods.
        """
        if ax is None:
            fig, axes = self.phi.plot(colorbar=colorbar,
                                      cb_orientation=cb_orientation,
                                      cb_label=cb_label, show=False, **kwargs)
            if show:
                fig.show()

            if fname is not None:
                fig.savefig(fname)
            return fig, axes

        else:
            self.phi.plot(colorbar=colorbar, cb_orientation=cb_orientation,
                          cb_label=cb_label, ax=ax, **kwargs)
Plot the phi component of the gravity field.

        Usage
        -----
        x.plot_phi([tick_interval, xlabel, ylabel, ax, colorbar,
                    cb_orientation, cb_label, show, fname, **kwargs])

        Parameters
        ----------
        tick_interval : list or tuple, optional, default = [30, 30]
            Intervals to use when plotting the x and y ticks. If set to None,
            ticks will not be plotted.
        xlabel : str, optional, default = 'longitude'
            Label for the longitude axis.
        ylabel : str, optional, default = 'latitude'
            Label for the latitude axis.
        ax : matplotlib axes object, optional, default = None
            A single matplotlib axes object where the plot will appear.
        colorbar : bool, optional, default = True
            If True, plot a colorbar.
        cb_orientation : str, optional, default = 'vertical'
            Orientation of the colorbar: either 'vertical' or 'horizontal'.
        cb_label : str, optional, default = '$g_\phi$, m s$^{-2}$'
            Text label for the colorbar.
        show : bool, optional, default = True
            If True, plot the image to the screen.
        fname : str, optional, default = None
            If present, and if axes is not specified, save the image to the
            specified file.
        kwargs : optional
            Keyword arguements that will be sent to the SHGrid.plot()
            and plt.imshow() methods.