The simplest method for measuring height is with an altimeter using air pressure to find height. When more precise measurements are needed, means like precise levels (also known as differential leveling) are used. When precise leveling, a series of measurements between two points are taken using an instrument and a measuring rod. Differences in height between the measurements are added and subtracted in a series to get the net difference in elevation between the two endpoints. With the Global Positioning System (GPS), elevation can be measured with satellite receivers. Usually GPS is somewhat less accurate than traditional precise leveling, but may be similar over long distances.
During the performance of a survey there may be many reasons why your surveyor is locating things that are not on your property. Surveyors in NC are required to “tie” their surveys to reference points that may or may not exist on your property. The verification of your property corners is done by locating other property corners and examining their location and their location given in the deeds and on the plats. If your property corners have been disturbed or removed it will be necessary to locate adjoining property corners in order to reestablish where your property corners belong.