diff --git a/data.yml b/data.yml
index fab9daa..03d10ae 100644
--- a/data.yml
+++ b/data.yml
@@ -90,26 +90,13 @@ Layer:
       max_size: 512
       password: osm
       port: 5432
-      srid: ''
-      table: |-
-        ( SELECT geom, type
-          FROM (
-              SELECT ST_Simplify(geom, 80000) AS geom, type FROM ice_z0
-              WHERE z(!scale_denominator!) BETWEEN 0 AND 1
-              UNION ALL
-              SELECT * FROM ice_z2
-              WHERE z(!scale_denominator!) BETWEEN 2 AND 4
-              UNION ALL
-              SELECT * FROM ice_z5
-              WHERE z(!scale_denominator!) BETWEEN 5 AND 8
-          ) AS ice
-          WHERE geom && !bbox!
-        ) AS t
+      srid: 900913
+      table: (SELECT * FROM layer_ice(!bbox!, z(!scale_denominator!))) AS t
       type: postgis
       user: osm
     description: Ice shelves
     fields: 
-      type: String
+      class: String
     properties: 
       "buffer-size": 4
     srs: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over
diff --git a/schema/layers/ice.sql b/schema/layers/ice.sql
index 89d187d..c6e31be 100644
--- a/schema/layers/ice.sql
+++ b/schema/layers/ice.sql
@@ -15,3 +15,19 @@ CREATE OR REPLACE VIEW ice_z5 AS (
     UNION ALL
     SELECT geom, 'ice_shelf' AS type FROM ne_10m_antarctic_ice_shelves_polys
 );
+
+CREATE OR REPLACE FUNCTION layer_ice(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, class text) AS $$
+    WITH zoom_levels AS (
+        SELECT ST_Simplify(geom, 80000) AS geom, type FROM ice_z0
+        WHERE zoom_level BETWEEN 0 AND 1
+        UNION ALL
+        SELECT * FROM ice_z2
+        WHERE zoom_level BETWEEN 2 AND 4
+        UNION ALL
+        SELECT * FROM ice_z5
+        WHERE zoom_level BETWEEN 5 AND 8
+    )
+    SELECT geom, type::text AS class FROM zoom_levels
+    WHERE geom && bbox;
+$$ LANGUAGE SQL IMMUTABLE;