Exploring Data from the NAVSTAR Global Positioning System (GPS)
A GPS receiver, using the U.S. Department of Defense NAVSTAR system of about 30 satellites, collects positional information—in the form of latitude, longitude, altitude, and time fixes—and stores these coordinates in its memory. Computer files of these points can then be made into Esri data sets.3
In November of 1994, students and faculty of the Department of Geography at the University of Kentucky participated in a cleanup of the Kentucky River. They took a GPS receiver on their trek; the antenna was mounted on the roof of a garbage scow (originally built as a houseboat).
One file the students collected, along the river from a marina to an “island” in the river, was C111315A.SSF (designating the 11th month, 13th day, 15th hour). Using post-processed differential correction, the files were adjusted to yield greater accuracy. The file was then converted to an Esri shapefile and renamed Boat_SP83.shp. The file is called Boat_SP83, since the dataset was projected to State Plane (Kentucky North Zone  coordinates, using the North American Datum of 1983 (NAD83 datum).