Add a buffer to the region of interest to keep stations around the edges and reduce edge effects in interpolation (and minimize differences at tile edges when stiching). I set the default distance to be 100km, but any value can be used.

https://projects.nceas.ucsb.edu/nceas/projects/environment-and-orga/repository/revisions/2b88b158f247e6205ebc5ca946c818eed2e6f42c