The GPS is not a perfect system. There are several types of errors that can occur when using the GPS receiver.

• Inputting incorrect information into a GPS receiver such as the datum, and when creating a waypoint.Unknowingly relying on a 2D position instead of a 3D position. This mistake can result in distance errors in excess of a mile. The signal from the satellite may be blocked by buildings, terrain, electronic interference. A GPS receiver needs a fairly clear sky to operate.
• The human body can cause signal interference.Holding a GPS receiver close to the body can block some satellite signals and hinder accurate positioning.

• Multipath interference is caused by the satellite signal reflecting off vehicles, buildings, power lines, water and other interfering objects. hen using a GPS receiver in a vehicle ,place the external antenna on the roof of the vehicle to eliminate signal interference.

These can be slight discrepancies in the satellite’s atomic clocks which may cause slight position errors in the GPS receiver. Errors are monitored and corrected by Master Control station.

Satellite orbits may vary due to gravitational pull and solar pressure fluctuations. Orbit errors are monitored and corrected by Master Control station.

The location of GPS satellites in relation to GPS receiver on ground can impact the receiver’s   ability to triangulate a 3D position. The quality decreases if the satellites are grouped close together in the sky above the receiver.

The atmosphere can speed up or slow down the satellite signal. Errors caused by atmospheric conditions has been reduced with the implementation of Wide Area Augmentation System.(WAAS).It is an experimental system which uses it own geostationary satellites positioned over the equator to transmit corrected GPS signals to receivers capable of receiving these signals.