diff --git a/pg/sql/0.0.1/03_overlap_sum.sql b/pg/sql/0.0.1/03_overlap_sum.sql
index f30f694..203be39 100644
--- a/pg/sql/0.0.1/03_overlap_sum.sql
+++ b/pg/sql/0.0.1/03_overlap_sum.sql
@@ -1,18 +1,36 @@
 -- Function by Stuart Lynn for a simple interpolation of a value
 -- from a polygon table over an arbitrary polygon
 -- (weighted by the area proportion overlapped)
+-- Aereal weighting is a very simple form of aereal interpolation.
+--
+-- Parameters:
+--   * geom a Polygon geometry which defines the area where a value will be
+--     estimated as the area-weighted sum of a given table/column
+--   * target_table_name table name of the table that provides the values
+--   * target_column column name of the column that provides the values
+--   * schema_name optional parameter to defina the schema the target table
+--     belongs to, which is necessary if its not in the search_path.
+--     Note that target_table_name should never include the schema in it.
+-- Return value:
+--   Aereal-weighted interpolation of the column values over the geometry
 CREATE OR REPLACE
-FUNCTION cdb_overlap_sum(geom geometry, target_table_name text, target_column text)
+FUNCTION cdb_overlap_sum(geom geometry, target_table_name text, target_column text, schema_name text DEFAULT NULL)
   RETURNS numeric AS
 $$
 DECLARE
 	result numeric;
+  qualified_name text;
 BEGIN
+  IF schema_name IS NULL THEN
+    qualified_name := Format('%I', target_table_name);
+  ELSE
+    qualified_name := Format('%I.%s', schema_name, target_table_name);
+  END IF;
   EXECUTE Format('
     SELECT sum(%I*ST_Area(St_Intersection($1, a.the_geom))/ST_Area(a.the_geom))
-    FROM %I AS a
+    FROM %s AS a
     WHERE $1 && a.the_geom
-  ', target_column, target_table_name)
+  ', target_column, qualified_name)
   USING geom
   INTO result;
   RETURN result;