What is GNIS you ask?
Once in a while we need to link data to certain sources. Depending on the source, the data that we are wanting to link to may use a certain "code", or numbering system, to identify things.
The Geographic Names Information System (GNIS) is the Federal and national standard for geographic nomenclature. The U.S. Geological Survey's National Geospatial Program developed the GNIS in support of the U.S. Board on Geographic Names as the official repository of domestic geographic names data, the official vehicle for geographic names use by all departments of the Federal Government, and the source for applying geographic names to Federal electronic and printed products.
This standard gives a number to every physical and cultural feature throughout the United States and it's associated areas. It is these numbers that give us a reference to the official name of these features. The GNIS is also a great source for the official GPS coordinates, Elevations, and other Federal Codes for each feature.