Hydrographic Event Management Tool
The USGS, USA, has released a web-based geospatial service known as the Hydrography Event Management (HEM) tool. It allows users to create, edit and display geospatial markers, called Events, that are referenced to the National Hydrography Dataset (NHD). Events can be customised by the user to represent almost any water-related feature.
Some examples of Events include streamgages, scenic or impaired stretches of river, fish passage barriers, toxic spills, or put-ins/take-outs for boats. For this initial release, users can customise their own HEM Web edit tool using a sample application and the required web services.
The use of events is a key characteristic of the NHD by allowing vast amounts of scientific information to be linked to the NHD while keeping the design simple and by making advanced analysis techniques possible. The HEM tool handles all the linear referencing mechanics to make working with events easy. It works on point, line, and area events and allows events to be located interactively, imported, or calculated. A Source Feature ID is created that provides the link between the event location and the informational data tied to the location. It also creates metadata linked to the event. The tool also provides network measuring to determine distances through the NHDFlowline network. The most current release of the tool is for ArcGIS 10.1 and NHD version 2.1.
