Module 1.2 Data Quality - Standards

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This week, still at Module 1 - Data Quality, we learned how to determine the accuracy of road networks using the methodology provided by the National Standard for Spatial Data Accuracy (NSSDA). The objective of this week's lab is to compare two different road network dataset, city level (ABQ) and national level (Street Map USA), in Albuquerque, New Mexico based on the NSSDA methodology. Based from experience, the city level usually provides a much more detailed information of the road network compared to the national level. This is because of the administrative level area that they usually work on has a smaller scale compared to a national level - which I think the national level generalizes their data most of the time. 

To start things off, we followed the 7 important steps of the NSSDA accuracy assessment (just using Steps 1 to 6). Here are the following steps:

STEP 1: Determine if the test needs horizontal (X and Y) accuracy, vertical (Z) or both.

STEP 2: Select your TEST points with a minimum of 20 to provide the best confidence level (95%). The points must be spaced 1/10 of the diagonal distance across the dataset and at least 20% of the points should be located in each quadrant. In this case, take note of the suitable locations for both the independent and test data with good intersections (right-angle) of your linear road networks. 

What I did in here was to use tessellation geoprocessing tool to come up with a 5x4 square and produce 20 points. This will satisfy the need of the points spaced at 1/10 and 20% location in each quadrant.

                                      

                                     

                                      

STEP 3: Use the orthoimagery data provided as the reference data as this has the highest accuracy among your dataset. 
                                            
                                            

STEP 4: Using the Generate XY data tool, determine your XY coordinates for you city, national and reference datasets (you will apply this to your 20 digitized and test points and not your road network).

STEP 5: Copy the information from your ArcGIS software and then paste the information usign the Excel worksheet provided. That will calculate a horizontal accuracy you need for your accuracy statement.

STEP 6: Report your accuracy statement - horizontal accuracy only as vertical accuracy is not applicable in this test module.
    • City ABQ Dataset: Tested 30.8 feet horizontal accuracy at 95% confidence level
    • StreetMapUSA Dataset: Tested 261.46 feet horizontal accuracy at 95% confidence level
STEP 7: Not required in this module.













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