Lab 3 M1.3 Data Quality - Assessment

 

Initial map showing visual difference

This week’s lab assignment was about Data Quality - Assessment, specifically road network quality and completeness. The information to work with is comprised of TIGER 2000 and Street Centerline data for roads in Jackson County, OR. The task is to determine the length of roads in each dataset in kilometers and which roads are more complete, 

When comparing datasets the first step is to make sure both are in the same coordinate system to ensure consistency. For each feature, the attribute table showed me what field should be measured to determine the total length of roads so summarizing the field length was next. I converted those results from international feet into kilometers. This was interesting because international feet are not as familiar to me as US survey feet, which are seen frequently in our lab datasets. These two are very similar but have differences in decimal spots that in results show greater precision and accuracy. 

After getting these results the next step is to measure the total length of both features within each grid. This was somewhat similar but I used the Summarize Within geoprocessing tool to get these results. The Grid was the input, and each road feature was the input summary. For the summary fields of the tool, I used the specific length fields to summarize the total length of the output. I added a field after spatially joining the two road files to determine the percentage of roads within each. The TIGER Road data are the more complete dataset over the Street Centerlines.

Total grids in which TIGER data are more complete: 165

Total grids in which Centerlines are more complete: 132

Road Length total of TIGER Roads: 11,253.5 KM

Road Length total of Centerlines Roads: 10,671.2 KM

The formula for calculating the results is:

% 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = (𝑡𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑒𝑛𝑡𝑒𝑟𝑙𝑖𝑛𝑒𝑠 − 𝑡𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑇𝐼𝐺𝐸𝑅 𝑅𝑜𝑎𝑑𝑠)/(𝑡𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑒𝑛𝑡𝑒𝑟𝑙𝑖𝑛𝑒𝑠) × 100%

The Street Centerline data “is intended for use as a reference map layer for GIS maps and applications and represents all known roads and trails within Jackson County, Oregon. The accuracy of this data is +/- 10 feet for state highways and in the urbanized portions of the county and +/- 30 feet in the remote rural areas.” (Street Centerlines Metadata) 

The TIGER data used is from 2000 with an accuracy of 5.975-6.531 meters for horizontal positional accuracy. Seo reminds us that “TIGER/Line data are produced by the US Census Bureau for 1:100,000 scale maps and contain various topographic features and administrative boundaries and their nominal accuracy is about 50 m (US Census Bureau 2000).” The dataset we used in this lab was gathered using a survey-grade GPS unit which used the same data but mapped it for greater accuracy.

Seo, Suyoung and O'Hara, Charles G.(2009) 'Quality assessment of linear data', International Journal of Geographical Information Science, 23: 12, 1503 — 1525, First published on: 22 September 2008 (iFirst) 

Final map showing percentage difference between roads