NHD Flowline Features - No Waterbodies (Legacy)

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）是一套基于地理要素的数据库，可对构成美国地表排水系统的河流河段或水系分段实现互联与唯一标识。该数据集最初以1:100000比例尺构建，全美范围均采用该比例尺数据。本次推出的高分辨率国家水文数据集通常以1:24000/1:12000比例尺制作，为原始1:100000比例尺的数据集补充了详细信息。（阿拉斯加、波多黎各及美属维尔京群岛的相关数据直接采用高分辨率模式构建，未使用1:100000比例尺。）针对已有合作方与数据源的区域，当前正推进本地化分辨率的国家水文数据集建设工作。国家水文数据集包含水系网络要素的河段编码、水流方向、水体名称，以及面状水体的中心线表征数据。该数据集同时针对各类水体以及五大湖、大西洋、太平洋与墨西哥湾的近似岸线划定了水系分段。此外，国家水文数据集还遵循了由联邦地理数据委员会（Federal Geographic Data Committee）制定的国家空间数据基础设施框架标准。