出典:Wikipedia
出典:『Wikipedia』 (2011/03/30 09:22 UTC 版)
The National Hydrography Dataset (NHD) is the surface water component of The National Map for the United States. It is used to represent surface water on maps and is also used to perform geospatial analysis. The NHD is a digital vector geospatial dataset designed for use in geographic information systems (GIS) for these two purposes. It contains features such as lakes, ponds, streams, rivers, canals, dams and streamgages that produce 7.5-million miles of streams/rivers and 6.5-million lake/ponds.