National Hydrography Dataset NHDFlowline layer with spatial representation of existing water uses defined in Title 25 Environmental Protection, Department of Environmental Protection, Chapter 93, Water Quality Standards. The Pennsylvania Code just cited provides a definition for distinguishing between designated and existing use classification. This GIS layer displays these uses spatially on an interactive stream map. Public users can drill down to locations on the map to view and map the existing uses of the water bodies of interest. The layer can also be used in conjunction with other spatially referenced data for spatial analyses.