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Data Quality

The goal of this analysis was to determine which road dataset (TIGER or Street Centerlines) was more complete for Jackson County, Oregon. Completeness in this case is defined by which dataset layer had a greater total length per grid subsection (267 grid subsections total) and greater coverage of the entire area of study. These two main points of my study were derived from the Haklay study.

”After gauging the level of positional accuracy of the OSM dataset, the next issue is the level of completeness. While Steve Coast, the founder of OSM, stated ``it's important to let go of the concept of completeness'' (GISPro, 2007, page 22), it is important to know which areas are well covered and which are notöotherwise, the data can be assumed to be unusable. ” (Haklay, 2009)

To begin with, I used the Summary Statistics tool to find the overall completeness of each layer within the study area. Tiger roads had a total of 11382.7 km of length while Street Centerlines only had 10873.3 km. In this first step, Street Centerlines is more complete.

Below are the steps I took to determine if TIGER or Street Centerlines was more complete per grid.

1.       I first reprojected the TIGER roads layer to the same projection as the Street roads layer in order to be able to compare the layers; reprojected to  NAD_1983_StatePlane_Oregon_South_FIPS_3602_Feet_Intl.

2.       Use the Clip tool to cut out any roads outside of the grid boundary areas. (I first tried to use the intersect tool but if failed to clip out the road features outside of the grid areas.) I used either the TIGER or Street roads layer as the input, and the Grid layer as the clip feature.

3.       I used the intersect tool on each of the TIGER/Street Centerline(SC) layers with the GRID layer to add the gridcode to the attribute table.

4.       Then I used the summarize within tool to determine the length of road per grid per TIGER/SC layer.

5.       I spatial joined both of the TIGER/SC summarized within layers to analyze them.

6.       I created a new field and used calculate field to determine how many grids had a greater road length in the SC layer over the TIGER layer (aka more completeness) and vice versa.

7.       I created a new field and plugged in the percent difference formula to find the percent difference.

8.       I changed the symbology to unique, manual to create a choropleth map of the percent difference.


I found that the Street Centerline was more complete at 61.4% (164 out of 267 grids) than the TIGER dataset that fell at 49.8% (133 out of 267 grids). While the Steet Centerline was more complete per grid overall, over the TIGER layer, it should be noted that TIGER did have greater overall completeness of area coverage for Jackson County.

Map 1: Percent Difference for Completeness Analysis of Jackson County, Oregon. 

Source: 

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. https://doi.org/10.1068/b35097


 

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