Making your first figure

Welcome to PyGMT! Here we’ll cover some of basic concepts, like creating simple figures and naming conventions.

Loading the library

All modules and figure generation is accessible from the pygmt top level package:

import pygmt

Creating figures

All figure generation in PyGMT is handled by the pygmt.Figure class. Start a new figure by creating an instance of this class:

fig = pygmt.Figure()

Add elements to the figure using its methods. For example, let’s start a map with an automatic frame and ticks around a given longitude and latitude bound, set the projection to Mercator (M), and the map width to 8 inches:

fig.basemap(region=[-90, -70, 0, 20], projection="M8i", frame=True)

Now we can add coastlines using pygmt.Figure.coast to this map using the default resolution, line width, and color:

fig.coast(shorelines=True)

To see the figure, call pygmt.Figure.show:

fig.show()

Out:

<IPython.core.display.Image object>

You can also set the map region, projection, and frame type directly in other methods without calling gmt.Figure.basemap:

fig = pygmt.Figure()
fig.coast(shorelines=True, region=[-90, -70, 0, 20], projection="M8i", frame=True)
fig.show()

Out:

<IPython.core.display.Image object>

Saving figures

Use the method pygmt.Figure.savefig to save your figure to a file. The figure format is inferred from the extension.

fig.savefig("central-america-shorelines.png")

Note for experienced GMT users

You’ll probably have noticed several things that are different from classic command-line GMT. Many of these changes reflect the new GMT modern execution mode that are part of GMT 6. A few are PyGMT exclusive (like the savefig method).

1. The name of method is coast instead of pscoast. As a general rule, all ps* modules had their ps prefix removed. The exceptions are: psxy which is now plot, psxyz which is now plot3d, and psscale which is now colorbar.

2. The arguments don’t use the GMT 1-letter syntax (R, J, B, etc). We use longer aliases for these arguments and have some Python exclusive names. The mapping between the GMT arguments and their Python counterparts should be straight forward.

3. Arguments like region can take lists as well as strings like 1/2/3/4.

4. If a GMT argument has no options (like -B instead of -Baf), use a True in Python. An empty string would also be acceptable. For repeated arguments, such as -B+Loleron -Bxaf -By+lm, provide a list: frame=["+Loleron", "xaf", "y+lm"].

5. There is no output redirecting to a PostScript file. The figure is generated in the background and will only be shown or saved when you ask for it.