The National Hydrogeologic Grid (NHG) dataset includes a raster and vector representation of 1-km cells defining a uniform grid that encompasses the continental United States. The value of each cell of the raster dataset corresponds to the 1-km cell number defined as 'cellnum' in the attributes of the vector data. The NHG consists of 4,000 rows and 4,980 columns, numbered from the top left corner of the grid, to correspond to the traditional row and column numbering system of the MODFLOW groundwater-flow simulation code (Hughes and others, 2017; Langevin and others, 2017). The Albers projection was chosen for the NHG because of the capability to best preserve area, which is crucial in the computation of volume for water-resource investigations (Kuniansky, 2016). The upper left coordinate of the NHG in the Albers projection, in units of meters, is -2553045.0, 3907285.0 with a rotation of zero degrees.
|Title||National-Scale Grid to Support Regional Groundwater Availability Studies and a National Hydrogeologic Framework|
|Authors||Brian R Clark, Paul M Barlow, Steven M. Peterson, Joseph D Hughes, Howard W Reeves, Roland Viger|
|Product Type||Data Release|
|Record Source||USGS Digital Object Identifier Catalog|
|USGS Organization||Office of Planning and Programming|