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HYDROGRAPHY The HYDRO coverages provide a digital representation of the surface water features mapped on standard 7.5-minute USGS quadrangles. The data was distributed by the USGS in Digital Line Graph (DLG) format. It was then processed in ARC/INFO to generate GRANIT data layers. The processing involved a series of steps, including assigning a GRANIT id to each feature, refining/streamlining attributes, and naming lakes/ponds. The modifications were made in conformance with standards adopted by the NH GIS Advisory Committee. The streamlined set of attributes allows users to identify lakes, ponds, wetlands, streams, intermittent streams, tidal bays, sewage and industrial impoundments, etc. In addition, feature names shown on standard quadrangles are being added to the coverage. The availability of the GRANIT id allows users to link back to the original full attribute list, if so desired, to generate additional data. For example, the full attribute list includes water surface elevations for a subset of the water bodies. As indicated on the status map, full coverage of the state is now available through the GRANIT database. Modifications, updates, and enhancements to the spatial and attribute data will continue to be made. Future plans call for features to be tagged with a second set of hydrologic codes that will permit hydrologic network analysis to be performed. In addition to the data documented above, statewide coverage of DLG-derived hydrography generated at 1:100,000 is available. This data may be used for large area, regional analyses. Primary Cover Name: HYDROnnn Cover Content: COMBINED HYDROGRAPHY Cover Type: POLYGON, LINE Source: DIGITAL LINE GRAPHS, USGS Source Scale: 1:24,000/1:25,000 Source Media: DIGITAL Automated By: US GEOLOGICAL SURVEY Coordinate Reference: NH State Plane Feet Horizontal Datum: 1983 Tile: 7.5-MINUTE QUADRANGLE Data Layer Last Revised: May, 1993 |
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