boundarynorm fix

doc/whats-new.rst

@@ -49,6 +49,8 @@ Deprecations
 Bug fixes
 ~~~~~~~~~
 
+- Proper plotting with BoundaryNorm type argument in :py:meth:`DataArray.plot(norm=matplotlib.colors.BoundaryNorm)`. (:issue:`4061`, :issue:`7014`,:pull:`7553`)
+  By `Jelmer Veenstra <https://github.com/veenstrajelmer>`_.
 - Improve error message when using in :py:meth:`Dataset.drop_vars` to state which variables can't be dropped. (:pull:`7518`)
   By `Tom Nicholas <https://github.com/TomNicholas>`_.
 - Require to explicitly defining optional dimensions such as hue

xarray/plot/utils.py

@@ -304,7 +304,7 @@ def _determine_cmap_params(
     if extend is None:
         extend = _determine_extend(calc_data, vmin, vmax)
 
-    if levels is not None or isinstance(norm, mpl.colors.BoundaryNorm):
+    if (levels is not None) and (not isinstance(norm, mpl.colors.BoundaryNorm)):
         cmap, newnorm = _build_discrete_cmap(cmap, levels, extend, filled)
         norm = newnorm if norm is None else norm
 

xarray/tests/test_plot.py

@@ -1194,6 +1194,13 @@ def test_discrete_colormap_provided_boundary_norm(self) -> None:
         primitive = self.darray.plot.contourf(norm=norm)
         np.testing.assert_allclose(primitive.levels, norm.boundaries)
 
+    def test_discrete_colormap_provided_boundary_norm_matching_cmap_levels(
+        self,
+    ) -> None:
+        norm = mpl.colors.BoundaryNorm([0, 5, 10, 15], 4)
+        primitive = self.darray.plot.contourf(norm=norm)
+        assert primitive.colorbar.norm.Ncmap == primitive.colorbar.norm.N
+
 
 class Common2dMixin:
     """