Integrated Hydrological Units of the United Kingdom View Service

This is a web map view service for the Integrated Hydrological Units (IHU) of the United Kingdom. The IHU define geographical reference units for hydrological purposes including river flow measurement and hydrometric data collection in the UK. The layers in this service represent the following component polygon layers: Hydrometric Areas with Coastline; Hydrometric Areas without Coastline; Groups; Sections; and Catchments. Each layer represents a different level of spatial detail. The coarsest level, Hydrometric Areas, is provided in two versions to meet differing user needs. Each Hydrometric Area is made up of one or more Groups. Each Group carries a name constructed from names of the major river flowing through the Group, the major river flowing into the Group, the major river into which the Group flows, and in some cases also from local county names. Each Group is made up of smaller units called Sections. A Section is the drainage area of a watercourse between two confluences. Only confluences of named watercourses were considered. Similarly to Groups, each Section carries a name constructed from names of the major river flowing through the Section, the major river flowing into the Section, and the major river into which the Section flows. Catchments represent the full area upstream from an outlet of every Section. Polygons within each layer do not have gaps and, with the exception of Catchments, polygons within one layer do not overlap. There are scale dependencies on this web map service which means that the Sections and Catchments layers are visible only at scales less than 1:250,000. The Hydrometric Areas with Coastline layer covers Great Britain and Northern Ireland, but all other layers currently cover Great Britain only as no dataset with river geometries and names with suitable detail is available for Northern Ireland.

本数据集为一项面向英国综合水文单元（IHU）的在线地图视图服务。综合水文单元（IHU）定义了用于水文目的的地理参照单元，包括河流流量测量和水位数据收集。该服务中的图层代表以下组成部分的多边形图层：沿海水文区域；非沿海水文区域；群体；段落；以及流域。每个图层代表不同的空间细节级别。最粗略的级别——水文区域，提供两种版本以满足不同用户的需求。每个水文区域由一个或多个群体组成。每个群体携带由通过群体的主要河流、流入群体的主要河流、群体流入的主要河流，以及在某些情况下还由当地县名构成的名字。每个群体由更小的单元——段落组成。段落是水道在两个汇合点之间的排水区域。仅考虑了命名水道的汇合点。与群体类似，每个段落也携带由通过段落的河流、流入段落的河流，以及段落流入的主要河流构成的名字。流域代表每个段落出口上游的全部区域。每个图层内的多边形无间隙，除流域外，同一图层内的多边形不重叠。该在线地图服务存在比例依赖性，这意味着段落和流域图层仅在比例小于1:250,000时可见。沿海水文区域图层覆盖大不列颠及北爱尔兰，但其他所有图层目前仅覆盖大不列颠，因为目前尚无适用于北爱尔兰的河流几何形状和名称的数据集。