Before revision:  The available implementation of GraphMaps system is based on an incremental mesh generation technique that does not control the number of zoom levels and the way the nodes appear on different levels .
After revision:  The available implementation of GraphMaps system is based on an incremental mesh generation technique that does not control the number of zoom levels may be large, nodes may be unevenly distributed to different levels, shared edges may create ambiguity due to the selection of multiple nodes .