Move to new modular layer structure

layers/building/building.sql

@@ -0,0 +1,22 @@
+CREATE OR REPLACE VIEW building_z13 AS (
+    SELECT osm_id, way, height, levels FROM buildings WHERE way_area > 1400
+);
+
+CREATE OR REPLACE VIEW building_z14 AS (
+    SELECT osm_id, way, height, levels FROM buildings
+);
+
+CREATE OR REPLACE FUNCTION layer_building(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, osm_id bigint, render_height float) AS $$
+    SELECT way, osm_id,
+    least(greatest(3, COALESCE(height, levels*3.66,5)),400)^.7 AS render_height
+    FROM (
+        SELECT osm_id, ST_Simplify(way, 10) AS way, height, levels FROM building_z13
+        WHERE zoom_level = 13 AND way && bbox
+        UNION ALL
+        SELECT * FROM building_z14
+        WHERE zoom_level >= 14 AND way && bbox
+    ) AS zoom_levels
+    ORDER BY render_height, ST_YMin(way) DESC;
+$$ LANGUAGE SQL IMMUTABLE;
+