To cite package ‘jpmap’ in publications use:

  Uchida M (2026). _jpmap: Japanese Prefectures_. R package version
  0.1.1, <https://github.com/uchidamizuki/jpmap>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {jpmap: Japanese Prefectures},
    author = {Mizuki Uchida},
    year = {2026},
    note = {R package version 0.1.1},
    url = {https://github.com/uchidamizuki/jpmap},
  }