diff --git a/layers/landcover/landcover.sql b/layers/landcover/landcover.sql
index a3549240..3123fc51 100644
--- a/layers/landcover/landcover.sql
+++ b/layers/landcover/landcover.sql
@@ -22,23 +22,23 @@ $$ LANGUAGE SQL IMMUTABLE;
 
 -- etldoc: ne_110m_glaciated_areas ->  landcover_z0 
 CREATE OR REPLACE VIEW landcover_z0 AS (
-    SELECT NULL::int AS osm_id, geom AS geometry, NULL AS landuse, 'glacier' AS "natural", NULL::text AS wetland FROM ne_110m_glaciated_areas
+    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'glacier'::text AS "natural", NULL::text AS wetland FROM ne_110m_glaciated_areas
 );
 
 CREATE OR REPLACE VIEW landcover_z2 AS (
     -- etldoc: ne_50m_glaciated_areas ->  landcover_z2 
-    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'glacier' AS "natural", NULL::text AS wetland FROM ne_50m_glaciated_areas
+    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'glacier'::text AS "natural", NULL::text AS wetland FROM ne_50m_glaciated_areas
     UNION ALL
     -- etldoc: ne_50m_antarctic_ice_shelves_polys ->  landcover_z2     
-    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'ice_shelf' AS "natural", NULL::text AS wetland FROM ne_50m_antarctic_ice_shelves_polys
+    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'ice_shelf'::text AS "natural", NULL::text AS wetland FROM ne_50m_antarctic_ice_shelves_polys
 );
 
 CREATE OR REPLACE VIEW landcover_z5 AS (
     -- etldoc: ne_10m_glaciated_areas ->  landcover_z5
-    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'glacier' AS "natural", NULL::text AS wetland FROM ne_10m_glaciated_areas
+    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'glacier'::text AS "natural", NULL::text AS wetland FROM ne_10m_glaciated_areas
     UNION ALL
     -- etldoc: ne_10m_antarctic_ice_shelves_polys ->  landcover_z5 
-    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'ice_shelf' AS "natural", NULL::text AS wetland FROM ne_10m_antarctic_ice_shelves_polys
+    SELECT NULL::bigint AS osm_id, geom AS geometry, NULL::text AS landuse, 'ice_shelf'::text AS "natural", NULL::text AS wetland FROM ne_10m_antarctic_ice_shelves_polys
 );
 
 CREATE OR REPLACE VIEW landcover_z8 AS (
diff --git a/layers/landuse/landuse.sql b/layers/landuse/landuse.sql
index c2cafbac..25361beb 100644
--- a/layers/landuse/landuse.sql
+++ b/layers/landuse/landuse.sql
@@ -10,20 +10,20 @@ $$ LANGUAGE SQL IMMUTABLE;
 
 -- etldoc: ne_50m_urban_areas -> landuse_z4
 CREATE OR REPLACE VIEW landuse_z4 AS (
-    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential' AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
+    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential'::text AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
     FROM ne_50m_urban_areas
     WHERE scalerank <= 2
 );
 
 -- etldoc: ne_50m_urban_areas -> landuse_z5
 CREATE OR REPLACE VIEW landuse_z5 AS (
-    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential' AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
+    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential'::text AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
     FROM ne_50m_urban_areas
 );
 
 -- etldoc: ne_10m_urban_areas -> landuse_z6
 CREATE OR REPLACE VIEW landuse_z6 AS (
-    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential' AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
+    SELECT NULL::bigint AS osm_id, geom AS geometry, 'residential'::text AS landuse, NULL::text AS amenity, NULL::text AS leisure, NULL::text AS boundary, scalerank
     FROM ne_10m_urban_areas
 );
 
diff --git a/layers/water/water.sql b/layers/water/water.sql
index 719e5b54..a6cc0df1 100644
--- a/layers/water/water.sql
+++ b/layers/water/water.sql
@@ -6,55 +6,55 @@ $$ LANGUAGE SQL IMMUTABLE;
 
 CREATE OR REPLACE VIEW water_z0 AS (
     -- etldoc:  ne_110m_ocean ->  water_z0 
-    SELECT geom, 'ocean' AS class FROM ne_110m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_110m_ocean
     UNION ALL
     -- etldoc:  ne_110m_lakes ->  water_z0     
-    SELECT geom, 'lake' AS class FROM ne_110m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_110m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z1 AS (
     -- etldoc:  ne_110m_ocean ->  water_z1    
-    SELECT geom, 'ocean' AS class FROM ne_110m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_110m_ocean
     UNION ALL   
     -- etldoc:  ne_110m_lakes ->  water_z1    
-    SELECT geom, 'lake' AS class FROM ne_110m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_110m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z2 AS (
     -- etldoc:  ne_50m_ocean ->  water_z2    
-    SELECT geom, 'ocean' AS class FROM ne_50m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_50m_ocean
     UNION ALL
     -- etldoc:  ne_50m_lakes ->  water_z2     
-    SELECT geom, 'lake' AS class FROM ne_50m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_50m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z4 AS (
     -- etldoc:  ne_50m_ocean ->  water_z4       
-    SELECT geom, 'ocean' AS class FROM ne_50m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_50m_ocean
     UNION ALL
     -- etldoc:  ne_50m_lakes ->  water_z4     
-    SELECT geom, 'lake' AS class FROM ne_50m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_50m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z5 AS (
     -- etldoc:  ne_10m_ocean ->  water_z5    
-    SELECT geom, 'ocean' AS class FROM ne_10m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_10m_ocean
     UNION ALL
     -- etldoc:  ne_10m_lakes ->  water_z5    
-    SELECT geom, 'lake' AS class FROM ne_10m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_10m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z6 AS (
     -- etldoc:  ne_10m_ocean ->  water_z6     
-    SELECT geom, 'ocean' AS class FROM ne_10m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_10m_ocean
     UNION ALL
    -- etldoc:  ne_10m_lakes ->  water_z6    
-    SELECT geom, 'lake' AS class FROM ne_10m_lakes
+    SELECT geom, 'lake'::text AS class FROM ne_10m_lakes
 );
 
 CREATE OR REPLACE VIEW water_z7 AS (
     -- etldoc:  ne_10m_ocean ->  water_z7     
-    SELECT geom, 'ocean' AS class FROM ne_10m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_10m_ocean
     UNION ALL
     -- etldoc:  osm_water_polygon_gen3 ->  water_z7     
     SELECT geometry AS geom, 'lake' AS class FROM osm_water_polygon_gen3
@@ -62,7 +62,7 @@ CREATE OR REPLACE VIEW water_z7 AS (
 
 CREATE OR REPLACE VIEW water_z8 AS (
     -- etldoc:  ne_10m_ocean ->  water_z8     
-    SELECT geom, 'ocean' AS class FROM ne_10m_ocean
+    SELECT geom, 'ocean'::text AS class FROM ne_10m_ocean
     UNION ALL
     -- etldoc:  osm_water_polygon_gen2 ->  water_z8         
     SELECT geometry AS geom, 'lake' AS class FROM osm_water_polygon_gen2
diff --git a/layers/waterway/waterway.sql b/layers/waterway/waterway.sql
index 29cb62c4..f8c3fa16 100644
--- a/layers/waterway/waterway.sql
+++ b/layers/waterway/waterway.sql
@@ -1,19 +1,19 @@
 
 -- etldoc: ne_110m_rivers_lake_centerlines ->  waterway_z3
 CREATE OR REPLACE VIEW waterway_z3 AS (
-    SELECT geom AS geometry, 'river' AS class FROM ne_110m_rivers_lake_centerlines
+    SELECT geom AS geometry, 'river'::text AS class FROM ne_110m_rivers_lake_centerlines
     WHERE featurecla = 'River'
 );
 
 -- etldoc: ne_50m_rivers_lake_centerlines ->  waterway_z4
 CREATE OR REPLACE VIEW waterway_z4 AS (
-    SELECT geom AS geometry, 'river' AS class FROM ne_50m_rivers_lake_centerlines
+    SELECT geom AS geometry, 'river'::text AS class FROM ne_50m_rivers_lake_centerlines
     WHERE featurecla = 'River'
 );
 
 -- etldoc: ne_10m_rivers_lake_centerlines ->  waterway_z6
 CREATE OR REPLACE VIEW waterway_z6 AS (
-    SELECT geom AS geometry, 'river' AS class FROM ne_10m_rivers_lake_centerlines
+    SELECT geom AS geometry, 'river'::text AS class FROM ne_10m_rivers_lake_centerlines
     WHERE featurecla = 'River'
 );