\BeginKnitrBlock{rmdnote}<div class="rmdnote">If you're running Mac or Linux, the previous command to install **sf** may not work first time.
These operating systems (OSs) have 'systems requirements' that are described in the package's [README](https://github.com/r-spatial/sf).
Various OS-specific instructions can be found online, such as the article *Installation of R 3.5 on Ubuntu 18.04* on the blog [rtask.thinkr.fr](https://rtask.thinkr.fr/blog/installation-of-r-3-5-on-ubuntu-18-04-lts-and-tips-for-spatial-packages/).</div>\EndKnitrBlock{rmdnote}