Module 1.2 Lab: Data Quality - Standards

 

This week’s assignment focused on performing a horizontal positional accuracy assessment of two street datasets: the City Streets layer and StreetMapUSA. The goal was to quantify how accurately each dataset represents the true locations of intersections using orthophotos as reference data. By selecting 20 representative test points, digitizing their true locations, and comparing them to the datasets, we calculated RMSE values and generated formal NSSDA accuracy statements. This exercise reinforced key GIS skills, including feature selection, digitizing reference points, coordinate extraction, and error analysis.

To assess this, 20 test points were selected across all quadrants of the study area. Reference points were digitized using orthophotos to represent the ‘true’ location of intersections. Coordinates for the reference points and corresponding points from both datasets were recorded. Differences in X and Y coordinates were calculated, Euclidean errors determined, and RMSE values computed to quantify horizontal accuracy following NSSDA guidelines.

Results:

The City Streets dataset has a horizontal accuracy of ±5.5 meters at the 95% confidence level.

The StreetMapUSA dataset has a horizontal accuracy of ±15.2 meters at the 95% confidence level.

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