NHD Areas

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 direction, 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.国家水文数据集（National Hydrography Dataset，NHD）是一款基于要素的数据库，可对构成美国地表排水系统的河段或水系片段进行互联与唯一标识。NHD数据最初以1:100000比例尺开发，全美范围均采用该比例尺数据。本高分辨率NHD通常以1:24000/1:12000比例尺开发，为原始1:100000比例尺的NHD补充了细节信息。（阿拉斯加、波多黎各及美属维尔京群岛的高分辨率数据并非采用1:100000比例尺开发。）本地分辨率NHD目前正在具备合作方与数据源的区域推进开发。NHD包含网络化要素的河段编码、流向、名称，以及面状水体的中心线表征形式。河段同时也在水体以及五大湖、大西洋、太平洋与墨西哥湾的近似岸线处进行定义。NHD同时遵循由联邦地理数据委员会制定的国家空间数据基础设施框架准则。