Hi. This is probably a really dumb question, by the way. I am calculating Moran's I on my data with ArcGIS 10 and I realized that it does not require you to generate a spatial weights matrix to run this - instead, inputing a spatial weights matrix is optional. How does it work if I do not input a weights matrix file? Does ArcGIS create a matrix on the fly or is something else going on that I don't understand? Thanks for any insight.