Precision vs. Accuracy

The textbook distinction between these two measures is very important when analyzing spatial data.  Precision, simply put, can be seen as how reliable something is measured; the more consistent the measurement is, the more precise.  Accuracy relates to how nearby something is to a known location.  To be accurate does not always equate to being precise and vice versa.  Determining which is more important when selecting GPS equipment can save a lot of money and explaining to whomever will be paying for the equipment and/or using the spatial data.

The distance from the Average Waypoint and the Reference point was observed at approximately 3.3 meters, whereas the estimated horizontal precision (68%) of the results is 4.5 meters.  Over one-meter separates these values and can be considered significant depending on the intent of the spatial data.  The GPS unit has better horizontal accuracy than it does precision.

The difference between the average elevation and the reference point elevation is 5.962 meters.  The estimated vertical precision (68%) of the results is 0.904 meters.  This is a significant difference between the two values; the GPS unit has more precise vertical precision than it does vertical accuracy.