GIS 5935 Lab 2

 This weeks lab was on Data Quality - Standards

We learned about various spatial data quality standards focusing on the National Map Accuracy Standards (NMAS), and National Standards for Spatial Data Accuracy (NSSDA). The NSSDA is one o the most recent standards to be issued by the Federal Geographic Data Committee (Minnesota Planning Land Management Information Center, 2019) Specific metrics that are used when measuring positional accuracy within these standards, such as: Sum; Average; Root Mean Square Error (RMSE); 68th, 90th, and/or 95th percentile. 

We were provided with 2 sets of street map data. We used orthophotos as reference to select and digitize a set of points (20) which we would use to test the accuracy of the two provided street map layers. The points chosen were primarily T-intersections. The points were equally distributed throughout the map. As our study area was relatively square I chose to divide it into four quadrants and select five points in each one.

Below you can see the even distribution of my manually selected reference points in yellow. The two provided street map layers are in pink and green.

X and Y coordinates were determined for all points, test and reference. The data from the attribute tables was then exported to excel and we utilized the Horizontal accuracy statistic worksheet from our provided Positional Accuracy Handbook .pdf. The horizontal accuracy worksheet had to be completed twice. Once for each set of test points obtained from the provided street map layers. Once the formulas were added and the calculations were completed the worksheets could be compared to see which map contained the most accurate data. We were tasked with putting our results into a formal accuracy statement (per NSSDA guidelines). The results match what I expected from the visual inspection of the data, the city of Albuquerque data was the most accurate of the two test sets.

Positional Accuracy: Tested 29.22 feet horizontal accuracy at 95% confidence level for the Albuquerque test points.

Positional Accuracy: Tested 369.68 feet horizontal accuracy at 95% confidence level for the Street Map USA test points.