PROJ 6 may impact workflows and packages using sf or rgdal
Changes introduced in PROJ 6, whether using the new proj.h API (sf) or the
old proj_api.h API (rgdal, lwgeom) may impact R workflows and packages
using sf or rgdal for transforming coordinate reference systems.
Because +datum= is effectively defunct, and will be gone in PROJ 7 (March
2020), any data including CRS set correctly for previous PROJ will risk no
longer be transformed correctly. Work is ongoing to establish how users
can adapt to this, but it will be very risky to assume that
transformations that worked in PROJ 4 will necessarily work as well or
better in PROJ >= 6 without manual intervention.
Please examine your workflows and packages, check whether your work is
affected, and contribute to discussions through the issues on github. This
list may be used, but it'll be best to keep things connected.