Monitoring - GIS Data

Chesapeake Bay SAV data were mapped from aerial imagery, primarily at a scale of 1:24,000, for the following regions: western shore, Va. only - 1971 & 1974; lower Bay, Va. only - 1980 & 1981; upper Bay, selected sections, 1979; Baywide, 1978, 1984 - 1987, and 1989 - 2016. Each area of SAV was classified into one of four density classes by the percentage of cover as determined from the aerial imagery (methodology is described in each annual report - e.g. see Orth et al., 2016). Starting in 2010, the SAV beds are stored as ArcGIS shapefiles using the quality control procedures documented in the individual metadata files. Data for prior years are stored as ArcInfo GIS coverages. Data were collected by the Virginia Institute of Marine Science and can be attributed by including a reference to the associated annual SAV distribution and abundance report.

The SAV data files for years prior to 2010 are in uncompressed ArcInfo (ESRI, Redlands, CA) export format. They have been compressed using pkzip compression to form .zip files for use on Windows-compatible personal computers and also compressed using unix standard compression to form .tar.Z files for use on unix platforms. Each file contains both the .e00 ARC/INFO export file and also a .txt metadata file. Starting in 2010, the .zip file contains a shapefile and metadata xml file. Please consult the metadata file to determine if a particular dataset will satisfy your needs.