ragreener1 [1] filed a request to merge r-geos [2] into r-rgeos [3]: rgeos is the name of the package on cran. Therefore, r-rgeos should be the name here.
[1] https://aur.archlinux.org/account/ragreener1/ [2] https://aur.archlinux.org/pkgbase/r-geos/ [3] https://aur.archlinux.org/pkgbase/r-rgeos/
