Add tile layer for regions with event count

tile-generator/layers/obs_regions/layer.sql

@@ -0,0 +1,26 @@
+DROP FUNCTION IF EXISTS layer_obs_regions(geometry, int);
+
+CREATE OR REPLACE FUNCTION layer_obs_regions(bbox geometry, zoom_level int)
+RETURNS TABLE(
+  region_id bigint,
+  geometry geometry,
+  name text,
+  admin_level int,
+  overtaking_event_count int
+) AS $$
+
+    SELECT
+      region.relation_id::bigint as region_id,
+      ST_SimplifyPreserveTopology(region.geometry, ZRes(zoom_level + 2)) as geometry,
+      region.name as name,
+      region.admin_level as admin_level,
+      count(overtaking_event.id)::int as overtaking_event_count
+    FROM region
+      LEFT JOIN overtaking_event on ST_Within(ST_Transform(overtaking_event.geometry, 3857), region.geometry)
+    WHERE
+      zoom_level >= 4 AND
+      zoom_level <= 12 AND
+      ST_Transform(region.geometry, 3857) && bbox
+    GROUP BY region.relation_id, region.name, region.geometry, region.admin_level
+
+$$ LANGUAGE SQL IMMUTABLE;

tile-generator/layers/obs_regions/obs_regions.yaml

@@ -0,0 +1,23 @@
+layer:
+  id: "obs_regions"
+  description: |
+      Statistics on administrative boundary areas ("regions")
+  buffer_size: 4
+  fields:
+    overtaking_event_count: |
+      Number of overtaking events.
+    name: |
+      Name of the region
+    admin_level: |
+      Administrative level of the boundary, as tagged in OpenStreetMap
+  defaults:
+    srs: EPSG:3785
+  datasource:
+    srid: 3857
+    geometry_field: geometry
+    key_field: region_id
+    key_field_as_attribute: no
+    query: (SELECT region_id, geometry, name, admin_level, overtaking_event_count FROM layer_obs_regions(!bbox!, z(!scale_denominator!))) AS t
+
+schema:
+  - ./layer.sql

tile-generator/openbikesensor.yaml

@@ -3,6 +3,7 @@ tileset:
   layers:
     - layers/obs_events/obs_events.yaml
     - layers/obs_roads/obs_roads.yaml
+    - layers/obs_regions/obs_regions.yaml
   version: 0.7.0
   id: openbikesensor
   description: >