public static FeatureGroup newInMemoryFeatureGroup(TileOrder tileOrder, Profile profile, PlanetilerConfig config,
    Stats stats) {
    return new FeatureGroup(FeatureSort.newInMemory(), tileOrder, profile, config, stats);
  }
Returns a feature grouper that stores all feature in-memory. Only suitable for toy use-cases like unit tests.
planetiler-core/src/main/java/com/onthegomap/planetiler/collection/FeatureGroup.java