To cite jpndistrict in publications, please use:

  S. Uryu (2017). jpndistirct: Create Japanese Administration Area and
  Office Maps. This map is based on the Digital Map 25000 (Map Image)
  published by Geospatial Information Authority of Japan (Approval
  No.603FY2017 information usage <http://www.gsi.go.jp>).

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {jpndistirct: Create Japanese Administration Area and Office Maps},
    author = {Shinya Uryu},
    year = {2017},
    url = {https://github.com/uribo/jpndistrict},
  }