Spatial polygons in
sf format for smoothing. Most of these polygons have
been created by converting rasters to polygons and therefore consist entirely
of right angles. There are examples of polygons with holes and multipart
sf object with 9 features and 3 attribute:
type: character; the geometry, i.e. "polygon" or "line".
hole: logical; whether the polygon has holes or not.
multipart: logical; whether the feature is single or multipart.