Plotting polygons

Plotting polygons is handled by the pygmt.Figure.plot method.

This tutorial focuses on input data given as NumPy arrays. Besides NumPy arrays, array-like objects are supported. Here, a polygon is a closed shape defined by a series of data points with x and y coordinates, connected by line segments, with the start and end points being identical. For plotting a geopandas.GeoDataFrame object with polygon geometries, e.g., to create a choropleth map, see the gallery example Choropleth map.

import numpy as np
import pygmt

Plot polygons

Set up sample data points as NumPy arrays for the x and y values.

x = np.array([-2, 1, 3, 0, -4, -2])
y = np.array([-3, -1, 1, 3, 2, -3])

Create a Cartesian plot via the pygmt.Figure.basemap method. Pass arrays to the x and y parameters of the pygmt.Figure.plot method. Without further adjustments, lines are drawn between the data points. By default, the lines are 0.25-points thick, black, and solid. In this example, the data points are chosen to make the lines form a polygon.

fig = pygmt.Figure()
fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
fig.plot(x=x, y=y)
fig.show()

The pen parameter can be used to adjust the lines or outline of the polygon. The argument passed to pen is one string with the comma-separated optional values width,color,style.

fig = pygmt.Figure()
fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
# Use a 2-points thick, darkred, dashed outline
fig.plot(x=x, y=y, pen="2p,darkred,dashed")
fig.show()

Use the fill parameter to fill the polygon with a color or pattern. Note, that there are no lines drawn between the data points by default if fill is used. Use the pen parameter to add an outline around the polygon.

fig = pygmt.Figure()
fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
# Fill the polygon with color "orange"
fig.plot(x=x, y=y, fill="orange")
fig.show()

Close polygons

Set up sample data points as NumPy arrays for the x and y values. Now, the data points do not form a polygon.

x = np.array([-2, 1, 3, 0, -4])
y = np.array([-3, -1, 1, 3, 2])

The close parameter can be used to force the polygon to be closed.

fig = pygmt.Figure()
fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
fig.plot(x=x, y=y, pen=True)

fig.shift_origin(xshift="w+1c")

fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
fig.plot(x=x, y=y, pen=True, close=True)
fig.show()

When using the fill parameter, the polygon is automatically closed.

fig = pygmt.Figure()
fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
fig.plot(x=x, y=y, pen=True)

fig.shift_origin(xshift="w+1c")

fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
fig.plot(x=x, y=y, pen=True, fill="orange")
fig.show()