_layerLengths = new int[2];
for (int ii=0; ii < 2; ii++) {
_layerSets.put(ii, new ArrayList<TileSetRecord>());
}
Iterator<Integer> tsids = tsrepo.enumerateTileSetIds();
while (tsids.hasNext()) {
Integer tsid = tsids.next();
TileSet set = tsrepo.getTileSet(tsid.intValue());
// determine which layer to which this tileset applies