private static LinearRing createFill(double buffer) {
    double min = -buffer;
    double max = buffer + 256;
    return GeoUtils.JTS_FACTORY.createLinearRing(GeoUtils.coordinateSequence(
      min, min,
      max, min,
      max, max,
      min, max,
      min, min
    ));
  }
If {@ocde exteriorRing} fills the entire tile, return the number of pixels that it overhangs, otherwise -1.
planetiler-core/src/main/java/com/onthegomap/planetiler/FeatureMerge.java