Support for unstructured grids (UGrids) began with GMS version 10. A variety of UGrids can be created using GMS. One type of UGrid is a Voronoi grid. A voronoi grid has certain desirable characteristics related to the computational scheme of MODFLOW-USG: MODFLOW-USG assumes that connected cells are perpendicularly bisected by a line connecting the centers of the cells. Recent enhancements to GMS 10.1 include a much faster Voronoi grid generator. An example model is shown below of a voronoi grid of the Biscayne Bay model area. This grid was generated in about 30 seconds on a core i7 3.4 GHz processor. The final grid has about 200,000 cells.