Expand Colorbar gallery example for categorical data (#2395)

Co-authored-by: Michael Grund <23025878+michaelgrund@users.noreply.github.com>

Author: yvonnefroehlich

examples/gallery/embellishments/colorbar.py

@@ -8,10 +8,10 @@
 can be found at :gmt-docs:`cookbook/cpts.html`. You can set the ``position`` of
 the colorbar using the following options:
 
-- **j/J**: justified inside/outside the map frame using any 2-character
+- **j/J**: placed inside/outside the map frame using any 2-character
   combination of vertical (**T**\ op, **M**\ iddle, **B**\ ottom) and
   horizontal (**L**\ eft, **C**\ enter, **R**\ ight) alignment codes, e.g.
-  ``position="jTR"`` for top right.
+  ``position="jTR"`` for Top Right.
 - **g**: using map coordinates, e.g. ``position="g170/-45"`` for longitude
   170E, latitude 45S.
 - **x**: using paper coordinates, e.g. ``position="x5c/7c"`` for 5 cm, 7 cm
@@ -21,15 +21,18 @@
 Note that the anchor point defaults to the bottom left (**BL**). Append ``+h``
 to ``position`` to get a horizontal colorbar instead of a vertical one.
 """
+
 import pygmt
 
 fig = pygmt.Figure()
 fig.basemap(region=[0, 3, 6, 9], projection="x3c", frame=["af", "WSne+tColorbars"])
 
+# ============
 # Create a colorbar designed for seismic tomography - roma
 # Colorbar is placed at bottom center (BC) by default if no position is given
 fig.colorbar(cmap="roma", frame=["x+lVelocity", "y+lm/s"])
 
+# ============
 # Create a colorbar showing the scientific rainbow - batlow
 fig.colorbar(
     cmap="batlow",
@@ -41,10 +44,11 @@
     scale=100,
 )
 
+# ============
 # Create a colorbar suitable for surface topography - oleron
 fig.colorbar(
     cmap="oleron",
-    # Colorbar position justified outside map frame (J) at Middle Right (MR),
+    # Colorbar placed outside map frame (J) at Middle Right (MR),
     # offset (+o) by 1 cm horizontally and 0 cm vertically from anchor point,
     # with a length/width (+w) of 7 cm by 0.5 cm and a box for NaN values (+n)
     position="JMR+o1c/0c+w7c/0.5c+n+mc",
@@ -55,4 +59,25 @@
     scale=10,
 )
 
+# ============
+# Create a colorbar suitable for categorical data - hawaii
+# Set up the colormap
+pygmt.makecpt(
+    cmap="hawaii",
+    series=[0, 3, 1],
+    # Comma-separated string for the annotations of the colorbar
+    color_model="+cA,B,C,D",
+)
+# Plot the colorbar
+fig.colorbar(
+    cmap=True,  # Use colormap set up above
+    # Colorbar placed inside map frame (j) at Bottom Left (BL),
+    # offset (+o) by 0.5 cm horizontally and 0.8 cm vertically from anchor
+    # point, and plotted horizontally (+h)
+    position="jBL+o0.5c/0.8c+h",
+    box=True,
+    # Divide colorbar into equal-sized rectangles
+    equalsize=0.5,
+)
+
 fig.show()