demote place nodes in admin areas

If a place node of city rank and above finds itself in an
administrative boundary of the same address rank, then
increase the address rank by 2. This catches the rather
frequent case where city suburbs are tagged for historical
reasons as towns or villages.

sql/functions/placex_triggers.sql

@@ -624,6 +624,21 @@ BEGIN
         NEW.rank_address := parent_address_level + 2;
       END IF;
     END IF;
+  -- If a place node is contained in a admin boundary with the same address level
+  -- and has not been linked, then make the node a subpart by increasing the
+  -- address rank (city level and above).
+  ELSEIF NEW.class = 'place' and NEW.osm_type = 'N'
+     and NEW.rank_address between 16 and 23
+  THEN
+    FOR location IN
+        SELECT rank_address FROM placex
+        WHERE osm_type = 'R' and class = 'boundary' and type = 'administrative'
+              and rank_address = NEW.rank_address
+              and geometry && NEW.centroid and _ST_Covers(geometry, NEW.centroid)
+        LIMIT 1
+    LOOP
+      NEW.rank_address = NEW.rank_address + 2;
+    END LOOP;
   ELSE
     parent_address_level := 3;
   END IF;