To cite package ‘PROJ’ in publications use:

Sumner M (2026). PROJ: Generic Coordinate System Transformations Using 'PROJ'. R package version 0.7.0, https://CRAN.R-project.org/package=PROJ.

Corresponding BibTeX entry:

  @Manual{,
    title = {PROJ: Generic Coordinate System Transformations Using
      'PROJ'},
    author = {Michael D. Sumner},
    year = {2026},
    note = {R package version 0.7.0},
    url = {https://CRAN.R-project.org/package=PROJ},
  }