I don't know the abstract for this talk, but it may be similar to the one for his talk at Swarthmore College, which I include here for your convenience:
Associated to any periodic tiling of the Euclidean plane is a certain finite, colored graph, called the "Delaney-Dress symbol" of the tiling. These graphs classify tilings in the sense that two tilings are equivalent if and only if their symbols are isomorphic. We will discuss algorithms that make use of this theory to systematically generate and visualize "all possible" periodic tilings of the Euclidean plane. A Macintosh application called RepTiles will be demonstrated.