Add a gallery example showing different colormaps in subplots (#1394)

Co-authored-by: Will Schlitzer <schlitzer90@gmail.com>
Co-authored-by: Michael Grund <23025878+michaelgrund@users.noreply.github.com>
Co-authored-by: Wei Ji <23487320+weiji14@users.noreply.github.com>

examples/gallery/embellishments/colorbars_multiple.py

@@ -0,0 +1,43 @@
+"""
+Multiple colormaps
+------------------
+This gallery example shows how to create multiple colormaps for different subplots. To
+better understand how GMT modern mode maintains several levels of colormaps,
+please refer to :gmt-docs:`cookbook/features.html#gmt-modern-mode-hierarchical-levels`
+for details.
+"""
+import pygmt
+
+fig = pygmt.Figure()
+
+# Load Earth relief data for the entire globe and a subset region
+grid_globe = pygmt.datasets.load_earth_relief(resolution="01d")
+subset_region = [-14, 30, 35, 60]
+grid_subset = pygmt.datasets.load_earth_relief(resolution="10m", region=subset_region)
+
+# Define a 1-row, 2-column subplot layout. The overall figure dimensions is set
+# to be 15 cm wide and 8 cm high. Each subplot is automatically labelled.
+# The space between the subplots is set to be 0.5 cm.
+with fig.subplot(
+    nrows=1, ncols=2, figsize=("15c", "8c"), autolabel=True, margins="0.5c"
+):
+    # Activate the first panel so that the colormap created by the makecpt
+    # method is a panel-level CPT
+    with fig.set_panel(panel=0):
+        pygmt.makecpt(cmap="geo", series=[-8000, 8000])
+        # "R?" means Winkel Tripel projection with map width automatically
+        # determined from the subplot width.
+        fig.grdimage(grid=grid_globe, projection="R?", region="g", frame=True)
+        fig.colorbar(frame=["a4000f2000", "x+lElevation", "y+lm"])
+    # Activate the second panel so that the colormap created by the makecpt
+    # method is a panel-level CPT
+    with fig.set_panel(panel=1):
+        pygmt.makecpt(cmap="globe", series=[-6000, 3000])
+        # "M?" means Mercator projection with map width also automatically
+        # determined from the subplot width.
+        fig.grdimage(
+            grid=grid_subset, projection="M?", region=subset_region, frame=True
+        )
+        fig.colorbar(frame=["a2000f1000", "x+lElevation", "y+lm"])
+
+fig.show()