Hydrology is a science of extremes; droughts and floods. In either case, the hydrologic response arises from the combination of many factors, such as terrain, land cover, land use, infrastructure, etc. Each has different, overlapping spatial domains. Superimposed upon these are temporal variations, driven by stochastic weather events that follow seasonal climatic regimes. To calculate risk (expected loss) requires a loss function (damage) and a response domain (flood depths) over which that loss is integrated. The watershed provides the spatial domain that collects all these factors. This talk will discuss the data used to characterize hydrologic response.