Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Anatomy of the Acronym: GPS

Global Anywhere on Earth — Well, almost anywhere, but not (or not as well):

• Inside buildings
• Underground
• In very severe precipitation
• Under heavy, wet tree canopy
• Around strong radio transmissions
• In “urban canyons” among tall buildings
• Near powerful radio transmitter antennas

or anywhere else that does not have a direct view of a substantial portion of the sky. The radio waves that GPS satellites transmit have very short lengths—about 20 cm. A wave of this length is good for measuring because it follows a very straight path, unlike its longer cousins, such as AM and FM band radio waves that may bend considerably. Unfortunately, short waves also do not penetrate matter very well, so the transmitter and the receiver must not have much solid matter between them, or the waves are blocked as light waves are easily blocked.

Positioning—Answering brand-new and age-old human questions: Where am I? How fast am I moving and in what direction? What direction should I go to get to some other specific location, and how long would it take at my current speed to get there? And, most importantly for GIS, where have I been? To collect GIS data with a GPS, one moves the receiver antenna around areas of the Earth, leaving a tracing of points in the memory of the receiver, which one later transfers to GIS software.

System—A collection of components with connections (links) among them. Components and links have characteristics. GPS might be divided up in the following ...