Use classes from ClearTables and add continents

layers/place/class.sql

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+CREATE OR REPLACE FUNCTION place_class(place TEXT)
+RETURNS TEXT AS $$
+    SELECT CASE
+        WHEN place IN ('city', 'town', 'village', 'hamlet', 'isolated_dwelling') THEN 'settlement'
+        WHEN place IN ('suburb', 'neighbourhood') THEN 'subregion'
+        WHEN place IN ('locality', 'farm') THEN 'other'
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE STRICT;
+
+CREATE OR REPLACE FUNCTION normalize_capital_level(capital TEXT)
+RETURNS INT AS $$
+    SELECT CASE
+        WHEN capital IN ('yes', '2') THEN 2
+        WHEN capital = '4' THEN 4
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE STRICT;