Currently the logic of the library utilizes nonZero filling rules for clipping with polygons, however, due to some mistake on my part it seems that multipolygons are not using nonzero intersections -- nor are unions. In the logic realm of mapnik if a multipolygon has two polygons that overlap they SHOULD have the same metadata therefore it seems wise that a nonzero fill policy is the proper solution here.
There are many different possible solutions with multipolygons so different fill patterns might make sense depending on the data but I think the most safe solution is most likely nonZero Filling.
Currently the logic of the library utilizes nonZero filling rules for clipping with polygons, however, due to some mistake on my part it seems that multipolygons are not using nonzero intersections -- nor are unions. In the logic realm of mapnik if a multipolygon has two polygons that overlap they SHOULD have the same metadata therefore it seems wise that a nonzero fill policy is the proper solution here.
There are many different possible solutions with multipolygons so different fill patterns might make sense depending on the data but I think the most safe solution is most likely nonZero Filling.