Module 1.2: Data Quality

 How accurate is data? 

Many times, we receive data, and as we make the assumption that the data is accurately applied into ArcPro, it is not always the case. The National Standard for Spatial Data Accuracy (NSSDA) creates a methodology to measure and describe the positional accuracy of data features. For our lab assignment, we were given two data sets for roads from USA street data and ABQ street data of Albuquerque, New Mexico.

In order to analyze the road data, we were instructed to create 20 points to serve as reference according to the areial imagery. Then gathering intersection points from the USA street data and the ABQ street data and gathering their XY coordinates to enter into excel to calculate SUM, AVERAGE, Root Mean Square Error (RMSE) values. 

SUM - The set of the squared differences between the test and the independent data sets. 

AVERAGE - The average of the sum. 

ROOT MEAN  SQUARE ERROR - The square root of the average.



To find the RMSE value at a 95% confidence level we need to times the RMSE value to 1.7308.

Notes: I had issues with my USA intersection data points as the RSME would not calculate because the average turned into a negative number and when I entered the formula =SQRT(AVERAGE(J2:J22)) it ended a $NUM error. As a result, my NSSDA numbers is very large. Due to the high nature of the value, the data from the USA has a significant scale error. Additional causes to the values in my USA data horizontal accuracy can possibly be how I sampled the data.  


We learned there is two was to summarize vertical and horizontal accuracy through a formal NSSDA (National Standard for Spatial Data Accuracy) and a detailed positional accuracy statement. The formal NSSDA accuracy statement explains that the data within a certain distance is at a 95% confidence is accurate. The detailed positional accuracy statement is used with the metadata. 
Formal Accuracy Statement

For the USA street data set: Tested 3442 feet horizontal accuracy at 95% confidence level. 

For the ABQ street data set: Tested 4.20 feet horizontal accuracy at 95% confidence level

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