To cite package ‘jpmap’ in publications use:

  Horiuchi Y (2026). _jpmap: Japan Maps with Insets for Okinawa and
  Ogasawara_. R package version 0.1.3,
  <https://CRAN.R-project.org/package=jpmap>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {jpmap: Japan Maps with Insets for Okinawa and Ogasawara},
    author = {Yusaku Horiuchi},
    year = {2026},
    note = {R package version 0.1.3},
    url = {https://CRAN.R-project.org/package=jpmap},
  }