Revamp water label display logic (#1457)

* At zooms 9-13, water labels will now be rendered for water features that are at least 0.25 tiles in size.  This means that water features that are the same size as a 128x128 pixel square will get a point label.
* Labels for large water features are now shown at the lowest zoom at which it's appropriate to show a label.
* Bay and strait names (`natural=bay` and `natural=strait`) are included. 
* Large seas modeled as areas (e.g. Caspian Sea) render as `class=sea` rather than `class=lake`

layers/water_name/update_water_point.sql

@@ -2,14 +2,22 @@ DROP TRIGGER IF EXISTS trigger_delete_point ON osm_water_polygon;
 DROP TRIGGER IF EXISTS trigger_update_point ON osm_water_polygon;
 DROP TRIGGER IF EXISTS trigger_insert_point ON osm_water_polygon;
 
+-- etldoc:  osm_water_polygon ->  osm_water_point_view
+-- etldoc:  lake_centerline ->  osm_water_point_view
 CREATE OR REPLACE VIEW osm_water_point_view AS
 SELECT wp.osm_id,
        ST_PointOnSurface(wp.geometry) AS geometry,
        wp.name,
        wp.name_en,
        wp.name_de,
+       CASE
+           WHEN "natural" = 'bay' THEN 'bay'
+           WHEN place = 'sea' THEN 'sea'
+           ELSE 'lake'
+       END AS class,
        update_tags(wp.tags, ST_PointOnSurface(wp.geometry)) AS tags,
-       ST_Area(wp.geometry) AS area,
+       -- Area of the feature in square meters
+       ST_Area(wp.geometry) as area,
        wp.is_intermittent
 FROM osm_water_polygon AS wp
          LEFT JOIN lake_centerline ll ON wp.osm_id = ll.osm_id
@@ -17,11 +25,25 @@ WHERE ll.osm_id IS NULL
   AND wp.name <> ''
   AND ST_IsValid(wp.geometry);
 
--- etldoc:  osm_water_polygon ->  osm_water_point
--- etldoc:  lake_centerline ->  osm_water_point
+-- etldoc:  osm_water_point_view ->  osm_water_point_earth_view
+CREATE OR REPLACE VIEW osm_water_point_earth_view AS
+SELECT osm_id,
+       geometry,
+       name,
+       name_en,
+       name_de,
+       class,
+       tags,
+       -- Percentage of the earth's surface covered by this feature (approximately)
+       -- The constant below is 111,842^2 * 180 * 180, where 111,842 is the length of one degree of latitude at the equator in meters.
+       area / (405279708033600 * COS(ST_Y(ST_Transform(geometry,4326))*PI()/180)) as earth_area,
+       is_intermittent
+FROM osm_water_point_view;
+
+-- etldoc:  osm_water_point_earth_view ->  osm_water_point
 CREATE TABLE IF NOT EXISTS osm_water_point AS
 SELECT *
-FROM osm_water_point_view;
+FROM osm_water_point_earth_view;
 DO
 $$
     BEGIN