DB Doc


Status of the National Geochemical Survey, 2008 September

The current status of sampling and analysis efforts by the NGS are shown in three maps below. These images contain information on the regions currently covered by the NGS, the types of sample media that were collected, the density of sampling, and plans for completing NGS coverage in the next few years. The present database contains analyses of 74,498 samples and 2,714 standards.
The image below shows the area of the United States currently covered by the NGS and for which data are available in this report. Colors are used to indicate which sample media are represented in different parts of the country. Note that overlapping symbols may obscure some points. At present, 89% of the land area of the US has sample coverage. 68% of the analyzed samples are stream sediments and the majority of the rest are soils.

(Click on map for larger version.)

The image below shows the density of geochemical sampling in the NGS.  Density is shown both as the number of samples per 1000 km2 (right side of legend) and as the approximate linear spacing between samples had they been collected along a perfect two-dimensional grid (left side of legend).  Hot colors indicate dense sampling and cool colors show areas where sampling is relatively sparse; white areas are not yet covered. Sample density is not uniform across the nation due to the incorporation of many different types of studies into the NGS (see descriptions of datasets), although a minimum density of ~1 sample per 289 km2 (dark blue) is maintained in all sampled areas (gray areas on the map, with lower densities, are not yet complete).  

(Click on map for larger version.)

The following image illustrates plans for completing the NGS. For planning purposes, the nation was divided into ~33,000 cells, each with ~289 km2 area.  These cells are shown in this map, color-coded by the status of sampling within the cell.  Green areas are done. Pale green cells were missed during initial phases of the NGS and may be filled at some future date.  In dark blue regions, collaborative sampling efforts by the USGS and state government agencies are under way.  Red areas include both cells that will probably not be sampled (e.g., the Nevada Test Site) and cells for which sampling plans have not yet been developed.

(Click on map for larger version.)