Introducing the “Gplot” Python module

`Gplot` is a (thin) wrapper around `matplotlib`, `basemap` and `cartopy` for quick and easy creations of geographical plots.

What’s this?

Gplot is a (thin) wrapper around matplotlib, basemap and cartopy for quick and easy creations of geographical plots. It is designed to create (almost) publish-ready figures with as few lines as possible, while preserving the possibility to fine-tune various aspects of the plots.

It is hosted at, and documentation here:

The creation of gplot

A few years ago, I switched from the vcs module of the CDAT package to the combination of matplotlib and basemap for my routine geographical plot creations. The motivation behind the switch is that vcs felt a bit primitive to me, with some rough edges here and there that the finished plots look not as polished as those created by matplotlib. For instance, it is a trivial task to create a multi-line plot in matplotlib, you just call the plt.plot() function multiple times (or plot all lines in one go). If you add a label each time and call the plt.legend() function at the end, you get a legend created for you, labeling all the lines in the plot.

To do the same thing in vcs is, however, miserably difficult. Calling the xvsy() function multiple times results in a mere superimposition of all the individual line plots onto the same canvas. By "mere superimposition" I literally meant it: all the line plots will have their own x- and y- axis extents (in matplotlib term, xlim and ylim) so that they won’t be aligned up to the same grid, and all the x- and y- axes ticks and labels are overlapping each other. All curves have the same color unless explicitly specified, and the legend will be put at the same location in the graph so that they all overlap with each other. It is totally unreadable, let alone publish-ready.

To be fair, vcs is more suited for creating geographical plots, but even those are less polished in my opinion. And often I needs to combine geographical plots with simple line plots in a single figure, as subplots, for instance, so I can’t easily use vcs for the former and matplotlib for the latter in a single graph.

So I made the switch to the matplotlib-basemap combo, and found it considerably easier in almost every aspect of my routine plot creation practices.

However, over time, I started to notice some inconveniences embedded in the matplotlib-basemap workflow. For instance, the API is a bit confusing regarding axis controls; colorbar placement can be a bit tricky, particularly if you want to achieve good spacings between plot elements (I have another post talking about this aspect); the map creation in basemap() requires too many lines. I recently discovered the proplot module and found that the author of which has made a pretty comprehensive summary of the "rough edges" of matplotlib, and I share many of the views with him.

To overcome the difficulties I encountered, I wrote some wrapper classes and functions in my spare time to help ease my everyday plot creation routines. In doing so, I did borrow the data-method-canvas syntax from vcs to form the gplot’s basic plotting syntax:

Plot2D(data, method, axis)

Where data is the input array – what to plot, method is the plotting method – how to plot, and axis the matplotlib axis object – where to plot.

The number of classes and functions grow over time, as I discovered more problems, I added more patches or new things to the collection, so a module-sized thing gradually came into being.

Then I decided maybe it would be not too bad an idea to properly format this thing into a module and share it. It started as a very personal little toolbox, but maybe it would also make sense to someone else, maybe someone else will find my creation useful as well.

So I spent about 2 weeks’ time clearing up the codes and reformatting things. And spent a few more days writing documentations etc.. Although still regarded as in early alpha, it is now on Github, and installable via conda:

conda install -c guangzhi gplot

What’s next

Considering the current user base of gplot is more or less just me myself, I will just keep on using it as a personal tool, making amendments here and there when needed. But I’m open to feature requests and code contributions.

It is planned to use cartopy as the default "backend" for geographical plots, as basemap has been deprecated. But cartopy still doesn’t feel quite ready, so I’m setting it aside for now.

It is also planned to make it easier to work with netCDF data read in by iris and xarray, but I’m not familiar with neither of them so they are not implemented yet. If you feel this thing useful and would like to contribute, please do!

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