This function is deprecated as of bcmaps 1.2.0, and will be removed in Summer 2023.
Use raster::union() for SpatialPolygonsDataFrames, or
sf::st_union() with sf objects instead.
The IDs of source polygons are stored in a list-column called
union_ids, and original attributes (if present) are stored as nested
dataframes in a list-column called union_df.
self_union(x)A SpatialPolygons or SpatialPolygonsDataFrame object
A SpatialPolygons or SpatialPolygonsDataFrame object