Legacy NHD Flowlines 2008

The following is excerpted from metadata provided by the USGS for the high-resolution NHD: "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 integrates the National Spatial Data Infrastructure framework criteria established by the Federal Geographic Data Committee." "The NHD is a national framework for assigning reach addresses to water-related entities, such as industrial discharges, drinking water supplies, fish habitat areas, wild and scenic rivers. Reach addresses establish the locations of these entities relative to one another within the NHD surface water drainage network, much like addresses on streets. Once linked to the NHD by their reach addresses, the upstream/downstream relationships of these water-related entities--and any associated information about them--can be analyzed using software tools ranging from spreadsheets to geographic information systems (GIS). GIS can also be used to combine NHD-based network analysis with other data layers, such as soils, land use and population, to help understand and display their respective effects upon one another. Furthermore, because the NHD provides a nationally consistent framework for addressing and analysis, water-related information linked to reach addresses by one organization (national, state, local) can be shared with other organizations and easily integrated into many different types of applications to the benefit of all."以下内容节选自美国地质调查局（USGS）针对高分辨率全国水文数据集（National Hydrography Dataset，简称NHD）提供的元数据：“全国水文数据集（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流河段进行互联与唯一标识。NHD原始数据以1:10万比例尺制作，且全美范围内均采用该比例尺的数据。本高分辨率NHD通常以1:2.4万/1:1.2万比例尺制作，为原始1:10万比例尺的NHD补充了更多细节信息。（阿拉斯加、波多黎各及美属维尔京群岛的高分辨率NHD数据未采用1:10万比例尺制作。）针对具备合作资源与数据基础的区域，本地化分辨率NHD数据正处于开发阶段。NHD包含网络化要素的河段编码、水流方向、水体名称，以及面状水体的中心线表达形式。河段的定义范围还覆盖了五大湖、大西洋、太平洋及墨西哥湾的水体与近似岸线区域。NHD同时遵循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，并完成相关整合。”“NHD是一套国家级框架，可用于为涉水实体分配河段地址，例如工业排污口、饮用水源地、鱼类栖息地、野生与风景河流等。河段地址可确定这些实体在NHD地表排水网络中的相对位置，与街道地址的作用原理类似。通过河段地址与NHD完成关联后，即可借助从电子表格到地理信息系统（Geographic Information Systems，简称GIS）的各类软件工具，分析这些涉水实体的上下游关系及其关联信息。GIS还可将基于NHD的网络分析结果与土壤、土地利用、人口等其他数据图层进行融合，以辅助理解并可视化展示各类要素间的相互影响。此外，由于NHD提供了全国统一的地址分配与分析框架，由国家级、州级或地方级机构通过河段地址关联的涉水信息，可与其他机构共享，并轻松集成至各类应用场景中，惠及所有相关方。”