private SpatialStrategy getSpatialStrategy(String key) {
SpatialStrategy strategy = spatial.get(key);
if (strategy==null) {
final int maxLevels = 11;
SpatialPrefixTree grid = new GeohashPrefixTree(ctx, maxLevels);
strategy = new RecursivePrefixTreeStrategy(grid, key);
spatial.put(key,strategy);
}
return strategy;
}