maptools retiring soon

[rsbivand]

See https://r-spatial.org/r/2022/04/12/evolution.html. From pkgapi analysis https://github.com/r-lib/pkgapi, this package uses elide() methods, which is used in R/transform.R. The maptools::elide() methods could be moved to sp, but I don't know whether this is worth doing given the restricted use in this package and no detected use elsewhere.