Ordering-based approaches (1,2) and quadtrees (3) have been introduced recently to detect multiple spatial clusters in point event datasets. The ALG (4) is an efficient graph-based data structure to handle the communication of cells in discrete domains. This adaptive data structure was favorably compared to common tree-based data structures (quadtrees). An additional feature of the ALG data structure is the total ordering of the component cells through a modified adaptive Hilbert curve, which links sequentially the cells (the orange curve in the example of Fig. 1 ).