To cite the USAboundaries package in publications, please cite the paper in the Journal of Open Source Software:

Mullen L, Bratt J (2018). “USAboundaries: Historical and Contemporary Boundaries of the United States of America.” Journal of Open Source Software, 3(23), 314. doi:10.21105/joss.00314, https://doi.org/10.21105/joss.00314.

Corresponding BibTeX entry:

  @Article{,
    title = {{USAboundaries}: Historical and Contemporary Boundaries of
      the United States of America},
    author = {Lincoln Mullen and Jordan Bratt},
    journal = {Journal of Open Source Software},
    year = {2018},
    volume = {3},
    number = {23},
    pages = {314},
    doi = {10.21105/joss.00314},
    url = {https://doi.org/10.21105/joss.00314},
  }