GIS5935 Module 1.3: Data Quality - Assessment

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A long weekend this week has been a nice way to catch up on several things in life, and makes staying on track in this course a little more easier. Speaking of long, this week was all about assessing road network quality through completeness. Now, how were road networks deemed complete? Well, we went at lengths for that. Literally! Haha.

Using a similar approach to the Haklay (2010) study, we compared two road networks, TIGER Roads and Street Centerlines, in Jackson County, Oregon by their total lengths in kilometers. Throughout the entire Jackson County, it was found that the TIGER Roads network had a longer length of roads than the Street Centerlines network, specifically 576.9km more.

As mentioned in Haklay's study, completeness was deemed by Van Oort as the "comprehensive... coverage of real-world objects" (Haklay, 2010, p. 685). In our case, we analyzed further than just total lengths alone to get a full understanding of road network completeness. Like in Haklay's study, we utilized grid cells to evaluate the study area of Jackson County into 5km x 5km sections. This allowed us to see patterns in which the road networks were equal or similar in their amount of road presence or if either one was greater in length. To calculate this road length amount per grid cell, we applied the following formula to get each grid cell's road length percent difference:

 % π‘‘π‘–π‘“π‘“π‘’π‘Ÿπ‘’π‘›π‘π‘’ = ((π‘‘π‘œπ‘‘π‘Žπ‘™ π‘™π‘’π‘›π‘”π‘‘β„Ž π‘œπ‘“ π‘π‘’π‘›π‘‘π‘’π‘Ÿπ‘™π‘–π‘›π‘’π‘  − π‘‘π‘œπ‘‘π‘Žπ‘™ π‘™π‘’π‘›π‘”π‘‘β„Ž π‘œπ‘“ 𝑇𝐼𝐺𝐸𝑅 π‘…π‘œπ‘Žπ‘‘π‘ ) / (π‘‘π‘œπ‘‘π‘Žπ‘™ π‘™π‘’π‘›π‘”π‘‘β„Ž π‘œπ‘“ π‘π‘’π‘›π‘‘π‘’π‘Ÿπ‘™π‘–π‘›π‘’π‘ )) × 100

Road Network Completeness in Jackson County, Oregon: A Tiger Roads & Street Centerlines Comparison. Using a muted orange to blue diverging symbology of 5 classes, you can see the areas in which TIGER or Centerlines had higher road length sums present per grid cell.

As shown in the map above, there are significant areas where TIGER had lengthier roads and is more complete than Street Centerlines. I opted to use a manual interval method with 5 classes. I believed any more than 5 classes for this analysis would make differentiating varying color shades difficult to pinpoint at a quick glance. To indicate the percentage difference, I chose an equal 40% increment between the classes for a symmetrical approach and balanced center value. I also selected a muted orange to blue diverging color scheme that would be easier on the eyes when trying to ascertain patterns.

Overall, I am fairly content with the map. Although, I wish I had more room to squeeze in a description/blurb like my previous map, but it would be too crowded in the space remaining. I especially wanted to keep the two insets to give greater context to the study area, specifically for terrain and elevation. You can see in the mountainous areas of Jackson County, there is a higher trend of Street Centerlines than TIGER, shown by the blue grid cells along the mountain ranges. On the other hand, TIGER was more predominant in flatter, urbanized areas, like Medford, where the orange cells are heavily concentrated.


References:

Haklay, M. (2010). How good is volunteered geographical information? A comparative study of OpenStreetMap and Ordnance Survey datasets. Environment and Planning B: Planning and Design, 37(4), 682–703.

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