To cite package ‘PROJ’ in publications use:

  Sumner M (2024). _PROJ: Generic Coordinate System Transformations
  Using 'PROJ'_. R package version 0.5.0,
  <https://CRAN.R-project.org/package=PROJ>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {PROJ: Generic Coordinate System Transformations Using 'PROJ'},
    author = {Michael D. Sumner},
    year = {2024},
    note = {R package version 0.5.0},
    url = {https://CRAN.R-project.org/package=PROJ},
  }