I just received a note from Hadley Wickham that a new version of ggplot2 is scheduled to be submitted to CRAN on June 25. Here’s what choroplethr users need to know about this new version of ggplot2.

Choroplethr Update Required

The new version of ggplot2 introduces bugs into choroplethr. In particular, choroplethr does not pass R cmd check when the new version of ggplot2 is loaded. I am planning to submit a new version of choroplethr to CRAN that addresses this issue prior to June 25.

This change is the third or fourth time I’ve had to update choroplethr in recent years as a result of changes to ggplot2. This experience reminds me of one of the first lessons I learned as a software engineer: “More time is spent maintaining old software than writing new software.”

Simple Features Support

One of the most common questions I get about choroplethr is whether I intend to add support for interactive maps. My answer has always been “I can’t do that until ggplot2 adds support for Simple Features.” Thankfully, this new version of ggplot2 introduces that support!

Currently all maps in the choroplethr ecosystem are stored as ggplot2 “fortified” dataframes. This is a format unique to ggplot2. Storing the maps in this format makes it possible to render the maps as quickly as possible. The downside is that:

1. ggplot2 does not support interactive graphics.
2. The main interactive mapping library in CRAN (leaflet) cannot render fortified data frames. It can only render maps stored as Shapefiles or Simple Features.

Once ggplot2 adds support for Simple Features, I can begin work on adding interactive map support to choroplethr. The first steps will likely be:

1. Updating choroplethr to be able to render maps stored in the Simple Features format.
2. Migrating choroplethr’s existing maps to the Simple Features format.

After that, I can start experimenting with adding interactive graphics support to choroplethr.

Note that Simple Features is not without its drawbacks. In particular, many users are reporting performance problems when creating maps using Simple Features and ggplot2. I will likely not begin this project until these issues have been resolved.

Thoughts on the CRAN Ecosystem

This issue has caused me to reflect a bit about the stability of the CRAN ecosystem. 

ggplot2 is used by about 1,700 packages. It’s unclear to me how many of these packages will have similar problems as a result of this change to ggplot2. And of the impacted packages, how many have maintainers who will push out a new version before June 25?

And ggplot2, of course, is just one of many packages on CRAN. This issue has the potential to occur whenever any package on CRAN is updated.

This issue reminded me that CRAN has a complex web of dependencies, and that package maintainers are largely unpaid volunteers. It seems like a situation where bugs can easily creep into an end user’s code.

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