The Global Positioning System
GPS is a satellite navigation system that allows users to locate their approximate position on Earth. There are 27 satellites orbiting Earth, as shown in the below picture, for use with GPS units. The satellites are positioned around Earth, and are constantly orbiting so that signals from at least three or four satellites can be picked up at any given moment by a GPS receiver.
To use GPS to find your location on Earth, you need a GPS receiver. The receiver calculates your approximate latitude and longitude — usually within 10 m — by processing the signals emitted by the satellites. If enough information is present, these satellites can also relay information about elevation, direction of movement, and speed.With signals from three satellites, a GPS receiver can calculate location on Earth without elevation, while four satellite signals will allow a GPS receiver to calculate elevation also. For more information on how the satellites are used to determine location, see as picturized below.
The Geographic Information System
The Geographic Information System (GIS) combines many of the traditional types and styles of mapping described in this chapter. GIS mapping uses a database of information gathered by scientists, professionals, and students like you from around the world to create layers, or “themes,” of information that can be placed one on top of the other to create a comprehensive map. These “themes” are often maps that were created with information gathered by remote sensing.
Scientists from many disciplines use GIS technologies. A geologist might use GIS mapping when studying a volcano to help track historical eruptions. An ecologist might use GIS mapping to track pollution or to follow animal or plant population trends of a given area.
GIS mapsmight contain many layers of information compiled from several different types of maps, such as a geologic map and a topographic map.As shown in the below picture,layers such as rivers, topography, roads,and landforms from the same geographic area can beplaced on top of each other to create a comprehensive map. One major difference between GIS mapping and traditional mapping is that a GIS map can be updated as new information is loaded into the database. Once a map is created, the layers are still linked to the original information. If this information changes, the GIS layers also change. The result is a map that is always up-to-date — a valuable resource for people who rely on current information.