Add waterway layer

layers/waterway/mapping.yaml

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+tables:
+  waterway_linestring:
+    type: linestring
+    fields:
+    - name: osm_id
+      type: id
+    - name: geometry
+      type: geometry
+    - name: waterway
+      key: waterway
+      type: string
+    - key: name
+      name: name
+      type: string
+    - name: name_en
+      key: name:en
+      type: string
+    mapping:
+      waterway:
+      - stream
+      - river
+      - canal
+      - drain
+      - ditch

layers/waterway/waterway.sql

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+CREATE OR REPLACE VIEW waterway_z3 AS (
+    SELECT geom, 'river' AS class FROM ne_110m_rivers_lake_centerlines
+    WHERE featurecla = 'River'
+);
+
+CREATE OR REPLACE VIEW waterway_z4 AS (
+    SELECT geom, 'river' AS class FROM ne_50m_rivers_lake_centerlines
+    WHERE featurecla = 'River'
+);
+
+CREATE OR REPLACE VIEW waterway_z6 AS (
+    SELECT geom, 'river' AS class FROM ne_10m_rivers_lake_centerlines
+    WHERE featurecla = 'River'
+);
+
+CREATE TABLE IF NOT EXISTS waterway_z8 AS (
+    SELECT ST_Simplify(geometry, 200) AS geom, waterway AS class FROM osm_waterway_linestring
+    WHERE waterway IN ('river') AND ST_Length(geometry) > 10000
+);
+CREATE INDEX IF NOT EXISTS waterway_z8_geom_idx ON waterway_z8 USING gist(geom);
+
+CREATE TABLE IF NOT EXISTS waterway_z9 AS (
+    SELECT ST_Simplify(geometry, 100) AS geom, waterway AS class FROM osm_waterway_linestring
+    WHERE waterway IN ('river') AND ST_Length(geometry) > 5000
+);
+CREATE INDEX IF NOT EXISTS waterway_z9_geom_idx ON waterway_z9 USING gist(geom);
+
+CREATE OR REPLACE VIEW waterway_z11 AS (
+    SELECT geometry AS geom, waterway AS class FROM osm_waterway_linestring
+    WHERE waterway IN ('river') AND ST_Length(geometry) > 5000
+);
+
+CREATE OR REPLACE VIEW waterway_z12 AS (
+    SELECT geometry AS geom, waterway AS class FROM osm_waterway_linestring
+    WHERE waterway IN ('river', 'canal') OR (waterway = 'stream' AND ST_Length(geometry) > 1000)
+);
+
+CREATE OR REPLACE VIEW waterway_z13 AS (
+    SELECT geometry AS geom, waterway AS class FROM osm_waterway_linestring
+    WHERE waterway IN ('river', 'canal', 'stream', 'drain', 'ditch') AND ST_Length(geometry) > 300
+);
+
+CREATE OR REPLACE VIEW waterway_z14 AS (
+    SELECT geometry AS geom, waterway AS class FROM osm_waterway_linestring
+);
+
+CREATE OR REPLACE FUNCTION layer_waterway(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, waterway text) AS $$
+    SELECT geom, class FROM (
+        SELECT * FROM waterway_z3 WHERE zoom_level = 3
+        UNION ALL
+        SELECT * FROM waterway_z4 WHERE zoom_level BETWEEN 4 AND 5
+        UNION ALL
+        SELECT * FROM waterway_z6 WHERE zoom_level BETWEEN 6 AND 7
+        UNION ALL
+        SELECT * FROM waterway_z8 WHERE zoom_level = 8
+        UNION ALL
+        SELECT * FROM waterway_z9 WHERE zoom_level BETWEEN 9 AND 10
+        UNION ALL
+        SELECT * FROM waterway_z11 WHERE zoom_level = 11
+        UNION ALL
+        SELECT * FROM waterway_z12 WHERE zoom_level = 12
+        UNION ALL
+        SELECT * FROM waterway_z13 WHERE zoom_level = 13
+        UNION ALL
+        SELECT * FROM waterway_z14 WHERE zoom_level >= 14
+    ) AS zoom_levels
+    WHERE geom && bbox;
+$$ LANGUAGE SQL IMMUTABLE;

layers/waterway/waterway.yaml

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+layer:
+  id: "waterway"
+  description: |
+      OpenStreetMap waterways.
+  buffer_size: 4
+  datasource:
+    query: (SELECT * FROM layer_waterway(!bbox!, z(!scale_denominator!))) AS t
+schema:
+  - ./waterway.sql
+datasources:
+  - type: imposm3
+    mapping_file: ./mapping.yaml