Add countries based on Natural Earth tiles

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;