update docs and change yincrease back to true

Author: Joe Hamman

doc/plotting.rst

@@ -158,6 +158,14 @@ and ``xincrease``.
     @savefig 2d_simple_yincrease.png width=4in
     air2d.plot(yincrease=False)
 
+.. note::
+
+    We use :py:func:`xray.plot.pcolormesh` as the default two-dimensional plot
+    method because it is more flexible than :py:func:`xray.plot.imshow`.
+    However, for large arrays, ``imshow`` can be much faster than ``pcolormesh``.
+    If speed is important to you and you are plotting a regular mesh, consider
+    using ``imshow``.
+
 Missing Values
 ~~~~~~~~~~~~~~
 

xray/plot/plot.py

@@ -331,7 +331,7 @@ def _plot2d(plotfunc):
 
     @functools.wraps(plotfunc)
     def newplotfunc(darray, x=None, y=None, ax=None, row=None, col=None,
-                    col_wrap=None, xincrease=None, yincrease=None,
+                    col_wrap=None, xincrease=True, yincrease=True,
                     add_colorbar=True, add_labels=True, vmin=None, vmax=None,
                     cmap=None, center=None, robust=False, extend=None,
                     levels=None, colors=None, subplot_kws=None, **kwargs):
@@ -434,7 +434,7 @@ def newplotfunc(darray, x=None, y=None, ax=None, row=None, col=None,
     # For use as DataArray.plot.plotmethod
     @functools.wraps(newplotfunc)
     def plotmethod(_PlotMethods_obj, x=None, y=None, ax=None, row=None,
-                   col=None, col_wrap=None, xincrease=None, yincrease=None,
+                   col=None, col_wrap=None, xincrease=True, yincrease=True,
                    add_colorbar=True, add_labels=True, vmin=None, vmax=None,
                    cmap=None, colors=None, center=None, robust=False,
                    extend=None, levels=None, subplot_kws=None, **kwargs):

xray/test/test_plot.py

@@ -707,7 +707,7 @@ def test_imshow_called(self):
         self.assertTrue(self.imshow_called(self.darray.plot.imshow))
 
     def test_xy_pixel_centered(self):
-        self.darray.plot.imshow()
+        self.darray.plot.imshow(yincrease=False)
         self.assertTrue(np.allclose([-0.5, 14.5], plt.gca().get_xlim()))
         self.assertTrue(np.allclose([9.5, -0.5], plt.gca().get_ylim()))