There are many methods of determining a position. If you have a gasoline station road map and see a road sign that indicates it is five miles to the next town, you can estimate your approximate position. If you have a more accurate product, such as a paper map or chart, or a digital image product from the National Geospatial-Intelligence Agency (NGA), you can get a better position. Electronic devices such as a Navstar Global Positioning System (GPS) satellite receiver can provide an extremely precise position. Precise positioning is needed to determine your exact current location (What is my starting point?) and/or your destination (Where is my target or ending point?).
These questions have different answers depending on your frame of reference and what you intend to do with the information. If you are in a hangar and want to move your airplane outside, you only need to know where you are with respect to the door. An eyeball estimate would be sufficient. It would not be necessary to know your location or the door's position to the nearest inch. The problem becomes a little more complicated if you are trying to put ordnance on target. In that case, you need to know your starting position very accurately as well as the target’s position very accurately. Hence, before asking "what is my position," you need to know to what accuracy you need the information and in what frame of reference.
Precision and Accuracy
Precision and accuracy are often used interchangeably, but in the targeting environment it is important to have high precision and high accuracy where the random and systematic errors are both small. The following picture illustrates the difference: