Use ClearTables scheme for classes

layers/transportation/class.sql

@@ -0,0 +1,34 @@
+CREATE OR REPLACE FUNCTION brunnel(is_bridge BOOL, is_tunnel BOOL, is_ford BOOL) RETURNS TEXT AS $$
+    SELECT CASE
+        WHEN is_bridge THEN 'bridge'
+        WHEN is_tunnel THEN 'tunnel'
+        WHEN is_ford THEN 'ford'
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE STRICT;
+
+-- The classes for highways are derived from the classes used in ClearTables
+-- https://github.com/ClearTables/ClearTables/blob/master/transportation.lua
+CREATE OR REPLACE FUNCTION highway_class(highway TEXT) RETURNS TEXT AS $$
+    SELECT CASE
+        WHEN highway IN ('motorway', 'motorway_link') THEN 'motorway'
+        WHEN highway IN ('trunk', 'trunk_link') THEN 'trunk'
+        WHEN highway IN ('primary', 'primary_link') THEN 'primary'
+        WHEN highway IN ('secondary', 'secondary_link') THEN 'secondary'
+        WHEN highway IN ('tertiary', 'tertiary_link') THEN 'tertiary'
+        WHEN highway IN ('unclassified', 'residential', 'living_street', 'road') THEN 'minor'
+        WHEN highway IN ('service', 'track') THEN highway
+        WHEN highway IN ('pedestrian', 'path', 'footway', 'cycleway', 'steps') THEN 'path'
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE STRICT;
+
+-- The classes for railways are derived from the classes used in ClearTables
+-- https://github.com/ClearTables/ClearTables/blob/master/transportation.lua
+CREATE OR REPLACE FUNCTION railway_class(railway TEXT) RETURNS TEXT AS $$
+    SELECT CASE
+        WHEN railway IN ('rail', 'narrow_gauge', 'preserved', 'funicular') THEN 'rail'
+        WHEN railway IN ('subway', 'light_rail', 'monorail', 'tram') THEN 'transit'
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE STRICT;