GEOG 160
Mapping Our Changing World



In Chapter 1, we discussed how geographic data rely on locational attributes and provided several examples demonstrating the importance of “place” in GIScience. One of the fastest growing uses of place information is for Location-Based Services (LBS) that take advantage of your phone’s ability to determine your location and, from that location, identify a wide array of nearby “services.” Using your smartphone to check in to your favorite restaurant would do very little if the device had no way to ‘know’ you were in the restaurant. Similarly, your phone could not help you find the nearest gas station while on a trip without knowing where you are at the time.

So, how does this happen - how does your phone know where you are? How can a radio collar detect a grizzly bear’s position and report it back to interested rangers? What, if anything, causes GPS to not work, and how can positional errors be corrected? This chapter will answer these questions and introduce the methods that make these technologies and processes possible.

Although tremendous technological advancements have occurred in the last century, the methods used to determine one’s position on the Earth pre-date satellites, the Internet, and smartphones. Readers of this chapter will trace the history of these technologies back to their foundations in land surveying and triangulation, acquiring knowledge about our incredible technologies and the basic concepts that drive them.


Students who successfully complete Chapter 5 should be able to:

  1. identify and define the key aspects of geographic data quality, including resolution, precision, and accuracy;
  2. explain how radio signals broadcast by Global Positioning System (GPS) satellites are used to calculate positions on the surface of the Earth;
  3. state the kinds and magnitude of error associated with uncorrected GPS positioning;
  4. identify and explain methods used to improve the accuracy of GPS positioning;
  5. list and explain the procedures land surveyors use to produce positional data, including traversing, triangulation, and trilateration.

Table of Contents

  • Geospatial Data Quality:Validity, Accuracy, and Precision
  • Global Positioning Systems
  • GPS Error Sources
  • Correcting GPS Errors
  • Land Surveying and Conventional Techinques for Measuring Positions on the Earth's Surface
  • Summary
  • Glossary
  • Biblography