Integer value(Object value) {
      Integer i = values.get(value);
      if (i == null) {
        i = values.size();
        values.put(value, i);
      }
      return i;
    }
Returns the ID associated with {@code value} or adds a new one if not present.
planetiler-core/src/main/java/com/onthegomap/planetiler/VectorTile.java