GIS5935 Module 1.3: Data Quality - Assessment

    The goal of the analysis for this week’s study on accuracy assessment was to determine which dataset, TIGER Roads or Street Centerlines, were more complete for Jackson County, Oregon.  In this lab, we are measuring completeness using the assumption that the more road there is, the more complete it is.

    We could use the length of the roads to determine completeness. After ensuring data was in the same projection, we looked at the statistics (Attribute Table -> Visualize Statistics) to determine the sum of the road segment lengths:

Street Centerline: 10873.3 km

TIGER Roads: 11382.7 km

Because this lab measures completeness based on road length (the more road there is, the more complete it is) – in this case, TIGER Roads is more complete than Street Centerline.

We went a little further in this lab to determine length of roads with each grid of Jackson County, Florida – see Map 1:

Map 1: Percent Difference of Road Length between TIGER Roads and Street Centerlines datasets of Jackson County, Oregon.


To determine road length per grid, the below steps were employed: 

Step 1: Use the Clip tool to remove road segments that lie outside the grid square boundaries.

-          Input Features: TIGER Roads or Street Centerline features

-          Clip Features: Grid

Step 2: Use Intersect tool on TIGER Roads and Street Centerline feature classes with the Grid feature class separately. This added the gridcode field to the TIGER Roads and Street Centerline feature classes.

Step 3: Use Summarize Within tool on TIGER Roads_Intersect  and Street Centerline_Intersect feature classes. This determined the length of the road segments.

Step 4: Use Spatial Join tool on TIGER Roads_Summarize and Street Centerline_Summarize  feature classes – this will allow us to determine whether Street Centerline or TIGER Roads in the next step had more or less road segment lengths over the other in the next step.

Step 5: In the Attribute Table of the spatially joined feature class, add New Field and use Calculate Field with the code: “!SCsum_Length_KILOMETERS! > !TIGERsum_Length_KILOMETERS!” – the resulting field will indicate:

1 = Street Centerline (SC) summarized length is greater than the TIGER Roads summarized length

0 = Street Centerline (SC) summarized length is less than the TIGER Roads summarized length

Results of Step 5:

142/297 grids = SC greater/more complete than TIGER Roads

155/297 grids = SC less complete than TIGER Roads

 

Results

47.8% of Street Centerline road segments were more complete (142 out of 297 grids).

52.2% of TIGER Roads were more complete (155 out of 297 grids).

 

Percent Difference

      

    =  -5.46% difference

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