This class is the union of several spatial objects from raster and sp packages.
Members:
RasterLayer, RasterLayerSparse, RasterStack;
SpatialLines, SpatialLinesDataFrame;
SpatialPixels, SpatialPixelsDataFrame;
SpatialPoints, SpatialPointsDataFrame;
SpatialPolygons, SpatialPolygonsDataFrame.
Notably missing is RasterBrick, for now.