To cite package ‘NipponMap’ in publications use:

Tanimura S (2018). NipponMap: Japanese Map Data and Functions. R package version 0.2, https://CRAN.R-project.org/package=NipponMap.

Corresponding BibTeX entry:

  @Manual{,
    title = {NipponMap: Japanese Map Data and Functions},
    author = {Susumu Tanimura},
    year = {2018},
    note = {R package version 0.2},
    url = {https://CRAN.R-project.org/package=NipponMap},
  }