Add countries based on Natural Earth tiles

data.yml

@@ -170,6 +170,31 @@ Layer:
     properties: 
       "buffer-size": 64
     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
+  - id: country
+    Datasource: 
+      dbname: osm
+      extent: -20037508.34,-20037508.34,20037508.34,20037508.34
+      geometry_field: geom
+      geometry_table: ''
+      host: db
+      key_field: ''
+      key_field_as_attribute: ''
+      max_size: 512
+      password: osm
+      port: 5432
+      srid: 900913
+      table: (SELECT * FROM layer_country(!bbox!, z(!scale_denominator!))) AS t
+      type: postgis
+      user: osm
+    description: Buildings
+    fields: 
+      abbrev: String
+      labelrank: Number
+      name: String
+      scalerank: Number
+    properties: 
+      "buffer-size": 64
+    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
 maxzoom: 14
 minzoom: 0
 name: OSM2VectorTiles v3.0

schema/layers/country.sql

@@ -0,0 +1,46 @@
+CREATE TABLE IF NOT EXISTS country_label AS (
+    SELECT topoint(geom) AS geom,
+           name,
+           adm0_a3, abbrev, postal,
+           scalerank, labelrank,
+           CASE WHEN tiny < 0 THEN 0 ELSE 1 END AS is_tiny
+    FROM ne_10m_admin_0_countries
+    WHERE scalerank <= 1
+);
+CREATE INDEX IF NOT EXISTS country_label_geom_idx ON country_label USING gist(geom);
+
+CREATE OR REPLACE VIEW country_z1 AS (
+    SELECT * FROM country_label WHERE scalerank = 0 AND is_tiny = 0 AND labelrank <= 2
+);
+
+CREATE OR REPLACE VIEW country_z2 AS (
+    SELECT * FROM country_label WHERE scalerank = 0 AND is_tiny = 0 AND labelrank <= 3
+);
+
+CREATE OR REPLACE VIEW country_z3 AS (
+    SELECT * FROM country_label WHERE scalerank = 0 AND is_tiny = 0
+);
+
+CREATE OR REPLACE VIEW country_z5 AS (
+    SELECT * FROM country_label WHERE scalerank <= 1
+);
+
+CREATE OR REPLACE FUNCTION layer_country(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, name text, abbrev text, postal text, scalerank int, labelrank int) AS $$
+    WITH zoom_levels AS (
+        SELECT * FROM country_z1
+        WHERE zoom_level = 1
+        UNION ALL
+        SELECT * FROM country_z2
+        WHERE zoom_level BETWEEN 2 AND 4
+        UNION ALL
+        SELECT * FROM country_z3
+        WHERE zoom_level BETWEEN 3 AND 4
+        UNION ALL
+        SELECT * FROM country_z5
+        WHERE zoom_level >= 5
+    )
+    SELECT geom, name, abbrev, postal, scalerank::int, labelrank::int FROM zoom_levels
+    WHERE geom && bbox
+    ORDER BY scalerank, labelrank, length(name);
+$$ LANGUAGE SQL IMMUTABLE;