The hydro layer was digitized from the 2002 Virginia Base Mapping Program (VBMP) imagery. This hydro layer includes rivers, streams, ponds, lakes, and other bodies of water. Attribution of this data set is limited. It does not indicate the directional flow of water. The image below shows the hydro layer (refer to left side of illustration in supplemental METADATA file for Hydrography) and the hydro layer superimposed on top of aerial photography (refer to right side of the illustration in supplemental METADATA file for Hydrography). Also note that only visible water resources were digitized. (Water passing below underpasses was not digitized). This data set is the most spatially accurate available, but it does not conform to National Hydrography Dataset (NHD) specifications (due to limitations associated with attribution, water flow, segmentation, and connectivity).
Intermittent streams are likely not contained in this file. Data was only collected in canals and ditches where water was visible (using aerial photography from spring 2002 . It should be noted that 2002 was an exceptionally dry spring in Virginia).
Ancillary data sets contained on this CD or from other sources (including the Digital Elevation Model (DEM), contour lines, and even the Digital Raster Graphic [DRG] can be integrated with this file to support the delineation of flow direction.
Spatial hydrologic features include:
Streams and Rivers Only streams with visible water will be collected. Streams will be single line up to 8 feet wide for 100 scale, or 30 feet wide for 200 and 400 scale. Double lines, representing left and right bank, will be collected where those dimensions are exceeded.
Lakes and Ponds Lakes and ponds will not be differentiated. Only lakes and ponds with visible water will be collected. The minimum dimension for collection is 100 feet in length or width.
Canals and Ditches Canals and ditches will not be differentiated. Only canals and ditches with visible water will be collected. Canals and ditches will be single line up to 8 feet wide for 100 scale, or 30 feet wide for 200 and 400 scale. Where those dimensions are exceeded, two lines will be placed, one to represent each bank.
Swamps and Marshes Swamps and marshes will not be differentiated. Only clearly identifiable swamps and marshes will be collected. The minimum dimension for collection is 1,000 feet in length or width.
Shorelines Shorelines for the Atlantic Ocean and Chesapeake Bay will be collected at the visible land/water interface. If the shoreline is bordered by tidal marsh, the shoreline will be collected at the land/marsh interface, not the marsh/water interface. Tidal marshes will be collected in Layer 4.
Data Type: Line/Polygon
Attribution: Very limited
-State Plane Virginia North or South (Contingent on locality, refer to index map in the Appendix)
-Linear Unit: US Foot
-Source: Virginia Geographic Information Network (VGIN)