This is often called metadata. Metadata are used to organize and maintain investments in data, to provide information to data catalogs and clearinghouses, and to aid data transfers. Many organizations within and outside of the federal government have adopted the FGDC metadata standard and are using automated indexing and serving mechanisms to provide access to their holdings through the Internet. Visit the FGDC Clearinghouse to learn more about how metadata is used in clearinghouses and to search for other data sets. Magnetic intensity is the strength of the magnetic field, and is described in terms of a horizontal component and a vertical component.
Vertical intensity is the vertical strength of the magnetic field.
These data are intended for geographic display and analysis at the national level, and for large regional areas. No responsibility is assumed by the U.S. Geological Survey in the use of these data. No explicit attempt was made to judge the accuracy of the lines with respect to the source gridded data. However, visual examination revealed that the lines portrayed are continuous and non-intersecting. This data set shows lines of equal vertical intensity for all of North America, including Greenland, Iceland, the Caribbean and most of Mexico.