Use only ne_10m_roads from Natural Earth #81

layers/transportation/class.sql

@@ -41,3 +41,13 @@ CREATE OR REPLACE FUNCTION service_value(service TEXT) RETURNS TEXT AS $$
         ELSE NULL
     END;
 $$ LANGUAGE SQL IMMUTABLE STRICT;
+
+-- Map Natural Earth types to OSM highway
+CREATE OR REPLACE FUNCTION ne_highway(type VARCHAR) RETURNS VARCHAR AS $$
+  SELECT CASE type
+    WHEN 'Major Highway' THEN 'motorway'
+    WHEN 'Secondary Highway' THEN 'trunk'
+    WHEN 'Road' THEN 'primary'
+    ELSE type
+  END;
+$$ LANGUAGE SQL IMMUTABLE;