Clarified return value of NumGeometries GIS function.
@@ -381,7 +381,9 @@ Accepts a single geographic field or expression and returns the memory size
Accepts a single geographic field or expression and returns the number of
geometries if the geometry field is a collection (e.g., a ``GEOMETRYCOLLECTION``
-or ``MULTI*`` field); otherwise returns ``None``.
+or ``MULTI*`` field). Returns 1 for single geometries.
+
+On MySQL, returns ``None`` for single geometries.
``NumPoints``
=============
