GIS Base Maps — GLOBAL POSITIONING SYSTEMS (GPS)

GPS is a tool we use for precise positioning of points on the earths surface using data transmitted from satellites 12,000 miles out in space. These satellites send out signals to our receiver (the thing on the tripod). The receiver(s) then transmits those signals to our data collector which stores the data. After we get it into the office, we download the data into the computer, and the computer software processes the data to an exact position of our survey points within a few millimeters. As the cost of the equipment continues to fall and the accuracy increases the use of GPS is becoming more and more favorable for land surveying applications. GPS is used for a number of different types of survey products. Large area control networks become more cost effective when utilizing GPS technology over conventional surveying methods. It reduces the time involved in gathering the required field data which translates into a cost saving on the overall project.

Although GPS is a very useful tool it does have limitations. For areas under tree cover or in the canyons of skyscraper buildings in large cities the satellite signals can be interrupted or blocked altogether. In these cases conventional survey methods and equipment are used to gather the field survey data. Also, contrary to popular belief by those practitioners not familiar with land surveying requirements for precision and accuracy, hand held GPS units are neither accurate nor precise enough to yield survey grade data. GPS technology serves a very useful purpose in the land surveying profession. The survey professional is responsible for applying the correct technology in a given situation or circumstance.