diff --git a/data.yml b/data.yml
index 611da25..544b1c0 100644
--- a/data.yml
+++ b/data.yml
@@ -87,42 +87,8 @@ Layer:
       max_size: 512
       password: osm
       port: 5432
-      srid: ''
-      table: |-
-        ( SELECT *
-          FROM (
-              SELECT * FROM boundary_z0 WHERE z(!scale_denominator!) = 0
-              UNION ALL
-              SELECT * FROM boundary_z1 WHERE z(!scale_denominator!) BETWEEN 1 AND 2
-              UNION ALL
-              SELECT * FROM boundary_z3 WHERE z(!scale_denominator!) = 3
-              UNION ALL
-              SELECT * FROM boundary_z4 WHERE z(!scale_denominator!) = 4
-              UNION ALL
-              SELECT * FROM boundary_z5 WHERE z(!scale_denominator!) BETWEEN 5 AND 6
-              UNION ALL
-              SELECT * FROM boundary_z7 WHERE z(!scale_denominator!) = 7
-              UNION ALL
-              SELECT ST_Simplify(geom, 400) AS geom, admin_level, scalerank, class
-              FROM boundary_z8 WHERE z(!scale_denominator!) = 8
-              UNION ALL
-              SELECT ST_Simplify(geom, 320) AS geom, admin_level, scalerank, class
-              FROM boundary_z8 WHERE z(!scale_denominator!) = 9
-              UNION ALL
-              SELECT ST_Simplify(geom, 150) AS geom, admin_level, scalerank, class
-              FROM boundary_z10 WHERE z(!scale_denominator!) = 10
-              UNION ALL
-              SELECT ST_Simplify(geom, 100) AS geom, admin_level, scalerank, class
-              FROM boundary_z10 WHERE z(!scale_denominator!) = 11
-              UNION ALL
-              SELECT ST_Simplify(geom, 50) AS geom, admin_level, scalerank, class
-              FROM boundary_z10 WHERE z(!scale_denominator!) = 12
-              UNION ALL
-              SELECT geom, admin_level, scalerank, class
-              FROM boundary_z10 WHERE z(!scale_denominator!) >= 13
-          ) AS admin
-          WHERE geom && !bbox!
-        ) AS data
+      srid: 900913
+      table: (SELECT * FROM layer_boundary(!bbox!, z(!scale_denominator!))) AS t
       type: postgis
       user: osm
     description: Buildings
diff --git a/schema/layers/boundary.sql b/schema/layers/boundary.sql
index 350cd7c..8833f17 100644
--- a/schema/layers/boundary.sql
+++ b/schema/layers/boundary.sql
@@ -85,3 +85,40 @@ CREATE OR REPLACE VIEW boundary_z10 AS (
     FROM admin_line
     WHERE level <= 8
 );
+
+CREATE OR REPLACE FUNCTION layer_boundary (bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, admin_level int, scalerank int, class text) AS $$
+    WITH zoom_levels AS (
+        SELECT * FROM boundary_z0 WHERE zoom_level = 0
+        UNION ALL
+        SELECT * FROM boundary_z1 WHERE zoom_level BETWEEN 1 AND 2
+        UNION ALL
+        SELECT * FROM boundary_z3 WHERE zoom_level = 3
+        UNION ALL
+        SELECT * FROM boundary_z4 WHERE zoom_level = 4
+        UNION ALL
+        SELECT * FROM boundary_z5 WHERE zoom_level BETWEEN 5 AND 6
+        UNION ALL
+        SELECT * FROM boundary_z7 WHERE zoom_level = 7
+        UNION ALL
+        SELECT ST_Simplify(geom, 400) AS geom, admin_level, scalerank, class
+        FROM boundary_z8 WHERE zoom_level = 8
+        UNION ALL
+        SELECT ST_Simplify(geom, 320) AS geom, admin_level, scalerank, class
+        FROM boundary_z8 WHERE zoom_level = 9
+        UNION ALL
+        SELECT ST_Simplify(geom, 150) AS geom, admin_level, scalerank, class
+        FROM boundary_z10 WHERE zoom_level = 10
+        UNION ALL
+        SELECT ST_Simplify(geom, 100) AS geom, admin_level, scalerank, class
+        FROM boundary_z10 WHERE zoom_level = 11
+        UNION ALL
+        SELECT ST_Simplify(geom, 50) AS geom, admin_level, scalerank, class
+        FROM boundary_z10 WHERE zoom_level = 12
+        UNION ALL
+        SELECT geom, admin_level, scalerank, class
+        FROM boundary_z10 WHERE zoom_level >= 13
+    )
+    SELECT geom, admin_level, scalerank::int, class FROM zoom_levels
+    WHERE geom && bbox;
+$$ LANGUAGE SQL;