Maps can only be as good as the data they are built upon, and data is only as useful if it is good data. One of the foundations of the National Map is the National Hydrography Dataset (NHD). The digital version of the blue lines on USGS topographic quad maps has evolved into a hearty dataset serving as the geospatial framework for the mapping, modeling, and planning of the nation’s water resources. The NHD is maintained in a rigorous process that utilizes technical mapping standards, custom tools, and a stewardship-maintenance system.
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