skip stuff if processupdates is no geometries were affected

src/c3nav/mapdata/utils/cache/changes.py

@@ -33,6 +33,10 @@ class GeometryChangeTracker:
             self._unary_unions[level_id] = union
         return union
 
+    @property
+    def is_empty(self):
+        return not self._geometries_by_level
+
     @property
     def area(self):
         return sum((self._get_unary_union(level_id).area