The National Hydrography Dataset (NHD) is a feature-based database that
interconnects and uniquely identifies the stream segments or reaches that
make up the nation's surface water drainage system. NHD data was originally
developed at 1:100,000-scale and exists at that scale for the whole
country. This high-resolution NHD, generally developed at 1:24,000/1:12,000 scale,
adds detail to the original 1:100,000-scale NHD. (Data for Alaska, Puerto Rico and
the Virgin Islands was developed at high-resolution, not 1:100,000 scale.) Local
resolution NHD is being developed where partners and data exist. The NHD contains
reach codes for networked features, flow directions, names, and centerline representations
for areal water bodies. Reaches are also defined on waterbodies and the approximate
shorelines of the Great Lakes, the Atlantic and Pacific Oceans and the Gulf of Mexico.
The NHD also incorporates the National Spatial Data Infrastructure framework criteria
established by the Federal Geographic Data Committee.
The New Hampshire NHD, or NHNHD, is an extract from the national dataset. The NH
Geological Survey at the NH Department of Environmental Services serves as the
custodian for the NH features in the NHD.