Positional Accuracy Standards

GIS 5935 Special Topics in GIS 
Lab 2

Learning Objectives:

• Learn how to determine the quality of road networks
• Determine the positional accuracy of two road networks by comparison
• Understand and employ the methodology of procedures provided by the National Standard for Spatial Data Accuracy (NSSDA)

Tools used:

• Create Fishnet
• Create Random Points
• Create Feature Class
• Create Features
• Add XY
• Table to Excel

Process

The National Standard for Spatial Data Accuracy (NSSDA) are guidelines for how to determine positional accuracy. There are 7 Steps in this process:

1. Determine if the test will be used to find horizontal accuracy, vertical accuracy, or both.

In our case, we are only interested in the horizontal accuracy. 

2. Select a set of test points:

20 random test points were determined. Test points were selected at intersections in order to be able to compare accuracy between data sets. These points needed to be recognizable between the ABQ (Bernalillo County , New Mexico street centerline shapefile) data sets and StreetMapUSA datasets

3. Select an independent dataset of higher accuracy:

Orthophotos with a six inch pixel resolution ( 1 pixel= 6 inches) was used as the reference data. This is of significantly higher resolution than either of the tested shapfiles. 

4. Collect Measurements:

Corresponding locations from each data set are digitized. Then the reference data points are digitized using the data selected in the last step. 

5. Calculate positional accuracy statistics using worksheet. 

6. Prepare an accuracy statement

   

7. Update Meta Data.