Module 1 GIS 5935 Special Topics in GIS 

Our first module for GIS 5935 has us learning about the difference between precision and accuracy and also the calculations and practices involved in determining precision and accuracy. It is a common misconception that precision and accuracy are the same thing, however something can be precise but still be inaccurate. In this weeks assignment we carried out analysis to determine the horizontal accuracy and precision of some data that was collected.

The first part of this weeks assignment had us determine the horizontal and vertical precision of points (from the same location) that were collected with a handheld GPS. The points were compared to a reference point that is the true location of the point that was collected. In order to carry out the analysis we had to carry out a batch processing operation to get all the coordinate systems in the same system, we had to do some field calculations and then we determined target percentiles for our data. Once we had target percentiles we had to create a buffer that showed where 50%, 68% and 95% of our data fell. We used the 68%  ring to determine our precision. Below is my resulting map with results. 

I calculated a horizontal precision of 4.5 meters and a vertical precision of 5.9 meters both at the 68% level. My calculated horizontal accuracy was 3.29 meters and my vertical accuracy was 5.96 meters. Horizontal precision was determined by coming up with an X,Y coordinate that was derived by averaging out all the collected waypoints. An index point was derived from the data and ring was created using the index point. The index point created a buffer which contained 68% of all the collected waypoints. The same method was used to determine the vertical precision. 

For accuracy a reference point was used and the the distance between the reference point and the average waypoint was used to determine the accuracy. The same methods were used to determine the vertical accuracy.