Special Topics - Lab 3 - Network Assessment

 Hello and welcome to Lab 3. This is the culmination of module 1, which explores the interrelated topics of standards, accuracy, precision, and finally a cumulative assessment. This lab evaluates the completeness of two different road networks covering Jackson County, Oregon. 

The two road networks being assessed are from two different sources. The area standard comes from the Jackson County GIS team and will be referenced as the Jackson Centerline feature. The comparison feature is a TIGER 2000 road layer. The assessment of these two features follows Hacklay's (2010) approach discussed in the article "How good is volunteered geographical information? A comparative study of OpenStreetMap and Ordnance Survey datasets" published in Environment and Planning B: Planning and Design 2010, volume 37, pages 682 - 703. 

Following that study there are two basic assessments: first, a simple length comparison of the two features. Completeness in that case is defined as whichever feature has greater length, which came from summarizing the total length of each segment. For the total county, the results were as follows: 

Jackson Centerline: 10,786.5 Km 
TIGER 2000: 11,253 Km

In this case, the TIGER network appears more substantive across Jackson County. 

The second assessment is a little more involved. following Hacklay, a Grid was applied to the County, specifically 297 5x5 Km grid cells. Both road networks were clipped to the grid, and then I determined the total length per cell. This allowed for each cell to be compared for individual completeness and a percentage difference between themselves. Interestingly, when only looking at the grided area, the summary results changed:

Jackson Centerline: 10,671 Km
TIGER 2000: 9,925.7 Km

Following Hacklay's presentation, the cells were determined as follows. 

Cells	Area
Jackson More Detailed (Longer)	163 of 297 cells = 55% or 4,075 SqKm
TIGER More Detailed (Longer)	123 of 297 cells = 41% or 3,075 SqKm
Cells approximately equal	11 of 297 cells = 4% or 275 Sqkm

While the procedures are discussed more in the map, the basic purpose of the grid is to highlight the percentage difference or length difference between the two layers. This was definitely an intensive amount of transformations of the original data and joining the results with the grid. This was a good culmination of all of the previous labs, looking at data accuracy, precision comparisons, and network completeness. Thank you.

v/r

Brandon