Add facetgrid_figsize option to set_options (#11103)

Add a new `facetgrid_figsize` option to `xr.set_options()` that controls
how FacetGrid determines figure size when `figsize` is not explicitly
passed. When set to `"rcparams"`, FacetGrid uses
`matplotlib.rcParams['figure.figsize']` instead of computing size from
`size` and `aspect`. Default is `"computed"` (current behavior).

Co-authored-by: Claude <noreply@anthropic.com>

Author: kkollsga

doc/whats-new.rst

@@ -155,6 +155,10 @@ Antonio Valentino, Chris Barker, Christine P. Chai, Deepak Cherian, Ewan Short,
 New Features
 ~~~~~~~~~~~~
 
+- Added ``facetgrid_figsize`` option to :py:func:`~xarray.set_options` allowing
+  :py:class:`~xarray.plot.FacetGrid` to use ``matplotlib.rcParams['figure.figsize']``
+  instead of computing figure size from ``size`` and ``aspect`` (:issue:`11103`).
+  By `Kristian Kollsga <https://github.com/kkollsga>`_.
 - :py:class:`~xarray.indexes.NDPointIndex` now supports coordinates with fewer
   dimensions than coordinate variables, enabling indexing of scattered points
   and trajectories where multiple coordinates (e.g., ``x``, ``y``) share a

xarray/core/options.py

@@ -40,6 +40,7 @@
         "use_numbagg",
         "use_opt_einsum",
         "use_flox",
+        "facetgrid_figsize",
     ]
 
     class T_Options(TypedDict):
@@ -73,6 +74,7 @@ class T_Options(TypedDict):
         use_new_combine_kwarg_defaults: bool
         use_numbagg: bool
         use_opt_einsum: bool
+        facetgrid_figsize: Literal["computed", "rcparams"]
 
 
 OPTIONS: T_Options = {
@@ -106,8 +108,10 @@ class T_Options(TypedDict):
     "use_new_combine_kwarg_defaults": False,
     "use_numbagg": True,
     "use_opt_einsum": True,
+    "facetgrid_figsize": "computed",
 }
 
+_FACETGRID_FIGSIZE_OPTIONS = frozenset(["computed", "rcparams"])
 _JOIN_OPTIONS = frozenset(["inner", "outer", "left", "right", "exact"])
 _DISPLAY_OPTIONS = frozenset(["text", "html"])
 _NETCDF_ENGINES = frozenset(["netcdf4", "h5netcdf", "scipy"])
@@ -144,6 +148,7 @@ def _positive_integer(value: Any) -> bool:
     "use_opt_einsum": lambda value: isinstance(value, bool),
     "use_flox": lambda value: isinstance(value, bool),
     "warn_for_unclosed_files": lambda value: isinstance(value, bool),
+    "facetgrid_figsize": _FACETGRID_FIGSIZE_OPTIONS.__contains__,
 }
 
 
@@ -222,6 +227,14 @@ class set_options:
     chunk_manager : str, default: "dask"
         Chunk manager to use for chunked array computations when multiple
         options are installed.
+    facetgrid_figsize : {"computed", "rcparams"}, default: "computed"
+        How :class:`~xarray.plot.FacetGrid` determines figure size when
+        ``figsize`` is not explicitly passed:
+
+        * ``"computed"`` : figure size is derived from ``size`` and ``aspect``
+          parameters (current default behavior).
+        * ``"rcparams"`` : use ``matplotlib.rcParams['figure.figsize']`` as the
+          total figure size.
     cmap_divergent : str or matplotlib.colors.Colormap, default: "RdBu_r"
         Colormap to use for divergent data plots. If string, must be
         matplotlib built-in colormap. Can also be a Colormap object
@@ -357,6 +370,8 @@ def __init__(self, **kwargs):
                     expected = f"Expected one of {_JOIN_OPTIONS!r}"
                 elif k == "display_style":
                     expected = f"Expected one of {_DISPLAY_OPTIONS!r}"
+                elif k == "facetgrid_figsize":
+                    expected = f"Expected one of {_FACETGRID_FIGSIZE_OPTIONS!r}"
                 elif k == "netcdf_engine_order":
                     expected = f"Expected a subset of {sorted(_NETCDF_ENGINES)}"
                 else:

xarray/plot/facetgrid.py

@@ -212,10 +212,17 @@ def __init__(
         subplot_kws = {} if subplot_kws is None else subplot_kws
 
         if figsize is None:
-            # Calculate the base figure size with extra horizontal space for a
-            # colorbar
-            cbar_space = 1
-            figsize = (ncol * size * aspect + cbar_space, nrow * size)
+            from xarray.core.options import OPTIONS
+
+            if OPTIONS["facetgrid_figsize"] == "rcparams":
+                import matplotlib as mpl
+
+                figsize = tuple(mpl.rcParams["figure.figsize"])
+            else:
+                # Calculate the base figure size with extra horizontal space
+                # for a colorbar
+                cbar_space = 1
+                figsize = (ncol * size * aspect + cbar_space, nrow * size)
 
         fig, axs = plt.subplots(
             nrow,

xarray/tests/test_options.py

@@ -84,6 +84,15 @@ def test_netcdf_engine_order() -> None:
     assert OPTIONS["netcdf_engine_order"] == original
 
 
+def test_facetgrid_figsize() -> None:
+    with pytest.raises(ValueError):
+        xarray.set_options(facetgrid_figsize="invalid")
+    with xarray.set_options(facetgrid_figsize="rcparams"):
+        assert OPTIONS["facetgrid_figsize"] == "rcparams"
+    with xarray.set_options(facetgrid_figsize="computed"):
+        assert OPTIONS["facetgrid_figsize"] == "computed"
+
+
 def test_display_style() -> None:
     original = "html"
     assert OPTIONS["display_style"] == original

xarray/tests/test_plot.py

@@ -3567,3 +3567,40 @@ def test_temp_dataarray() -> None:
     locals_ = dict(x="x", extend="var2")
     da = _temp_dataarray(ds, y_, locals_)
     assert da.shape == (3,)
+
+
+@requires_matplotlib
+def test_facetgrid_figsize_rcparams() -> None:
+    """Test that facetgrid_figsize='rcparams' uses matplotlib rcParams."""
+    import matplotlib as mpl
+
+    da = DataArray(
+        np.random.randn(10, 15, 3),
+        dims=["y", "x", "z"],
+        coords={"z": ["a", "b", "c"]},
+    )
+    custom_figsize = (12.0, 8.0)
+
+    with figure_context():
+        # Default behavior: computed from size and aspect
+        g = xplt.FacetGrid(da, col="z")
+        default_figsize = g.fig.get_size_inches()
+        # Default should be (ncol * size * aspect + cbar_space, nrow * size)
+        # = (3 * 3 * 1 + 1, 1 * 3) = (10, 3)
+        np.testing.assert_allclose(default_figsize, (10.0, 3.0))
+
+    with figure_context():
+        # rcparams mode: should use mpl.rcParams['figure.figsize']
+        with mpl.rc_context({"figure.figsize": custom_figsize}):
+            with xr.set_options(facetgrid_figsize="rcparams"):
+                g = xplt.FacetGrid(da, col="z")
+                actual_figsize = g.fig.get_size_inches()
+                np.testing.assert_allclose(actual_figsize, custom_figsize)
+
+    with figure_context():
+        # Explicit figsize should override the option
+        with xr.set_options(facetgrid_figsize="rcparams"):
+            explicit_size = (6.0, 4.0)
+            g = xplt.FacetGrid(da, col="z", figsize=explicit_size)
+            actual_figsize = g.fig.get_size_inches()
+            np.testing.assert_allclose(actual_figsize, explicit_size)