coord_geo_polar()

[willgearty]

It would be interesting to have a version of coord_geo() that extends the functionality of coord_polar() (source here) for circular plots. I imagine this would be almost exclusively used for circular/fan phylogenies, so might be easier to just build on top of something that's already in ggtree (https://github.com/YuLab-SMU/ggtree/blob/master/R/layout.R).