Gallery example "Legend": Update regarding input data and multi-column legends

[yvonnefroehlich]

Description of proposed changes

In contrast to the change in PR #2606, it is actually possible to create a multi-column legend for a automatically created legend. This PR corrects the introduction text of the gallery example "Legend".

I feel it would be good to show how to create a horizontal legend, as this is done via the label parameter of Figure.plot, and not via a parameter of the Figure.legend method. For more complicated adjustments of a legend a tutorial seem to make sense. Currently, the same plot is created twice, first with a vertical legend (default) and then with a horizontal legend. However, I am not 100 % happy with this example. I do not like that we plot the same data twice above each other, just with different symbols. And maybe it is not optimal to simply repeat the same plot. Suggestions are welcome 🙂.

Related:

• PyGMT issue: Multiple legend columns #2603
• PyGMT PR: Mention GMT docs regarding more complicated legends in gallery example "Legends" #2606
• GMT forum: https://forum.generic-mapping-tools.org/t/horizontal-legend/4362

Preveiw: https://pygmt-dev--2762.org.readthedocs.build/en/2762/gallery/embellishments/legend.html

Reminders

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• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

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[seisman]

However, I am not 100 % happy with this example. I do not like that we plot the same data twice above each other, just with different symbols. And maybe it is not optimal to simply repeat the same plot.

I agree. Maybe we can simply create some simple sine/cosine curves instead.

[yvonnefroehlich]

However, I am not 100 % happy with this example. I do not like that we plot the same data twice above each other, just with different symbols. And maybe it is not optimal to simply repeat the same plot.

I agree. Maybe we can simply create some simple sine/cosine curves instead.

I made some changes regarding the used data (now sine and cosine curves) and the shown legend (now vertical and horizontal legends). I combined this within one figure, a bit similar to the gallery example we have for colorbars. @GenericMappingTools/pygmt-maintainers, what do you think?

[seisman]

Is this PR still WIP? It looks good to me so approve.

[yvonnefroehlich]

Is this PR still WIP? It looks good to me so approve.

The PR should be finished from my side - updated the title. Just reduced some double blank lines.

@seisman I am sorry for accidentally writing in your comment 🙁 - I reverted this change.