Lab 6 Topic 3 Scale Effect and Spatial Data Aggregation

 Part 1b Scale Effects on Vector and Raster Data

This week’s lab was determining the effect of scale and resolution on vector and raster data. Another lab part was analyzing boundaries with Modifiable Area Unit Problem (MAUP), this involved looking at Gerrymandering in U.S. Congressional Districts.

For the vector data, the scale of data was 1:1200, 1:24000, and 1:100000. Because maps have different scales, a greater emphasis should be put on ensuring spatial accuracy is adhered to as much as possible. Understanding the effect of scale and resolution on vector data differs from observing raster data. 

In the first part of the lab, we used the Clip tool for our hydrography datasets with the county as the “clip to” feature. After clipping all the data to the county, we added fields and calculated geometry to get length, area, and total count.

As resolution decreases, the accuracy and details diminish. Scale expresses the amount of detail for vector data; the hydrographic features are polylines and vector data. Because the large scale map has more detail and the small scale has less detail, these show how the relationship between scale and these hydrography data are affected.

Map Scale 1:1500 Scale and resolution effects

Map Scale 1:20,000

Part 2b Gerrymandering

The Merriam-Webster Dictionary defines gerrymandering as “dividing or arranging a territorial unit into election districts in a way that gives one political party an unfair advantage in elections.” Its history dates back to the early 1800s when it became official and later defined but was known prior to this time. The Modifiable Areal Unit Problem (MAUP) is an issue with boundaries and scale in spatial analysis. It highlights potential issues of delineation, creating bias within voting areas, i.e., congressional districts. In this final part of the lab, the feature class consisted of the continental U.S. I used the Dissolve tool to amalgamate the districts and in doing so I was able to find out the number of polygons each Congressional District (CD) consisted of. The below picture is of CD 01, the compactness score from the Polsby-Popper test was the lowest of all the districts we looked at in this lab. It is the "worst offender" of having bizarre-shaped legislative districts.

Congressional District 01