USGS Gap Analysis Project Additional Data: Hydrography

Water and its location on the landscape are important aspects of a species distribution. A number of water related data layers were used to refine these USGS Gap Analysis Project species models. These include water type (i.e. flowing, open/standing), distance to and from water, and stream flow and underlying gradient. The source for this data was the USGS National Hydrography Dataset (NHD)(USGS 2007). Hydrographic features were divided into three types: flowing water, open/standing water, and wet vegetation. These feature types were extracted from the NHD by selecting the corresponding codes (the FCODE attribute) in datatables and creating seperate datasets for each data type. To facilitate their use in spatial modeling, these feature types were converted into grids and combined into 16 catagories where feature types overlapped. For each region there is the possiblity of having up to 21 different hydrographic buffer layers and within a model it is possible to have up to 72 different permutations of these layers.