Scale and Gerrymandering

 This week, we reviewed how scale affects our analysis and understanding of vector data and the basic resolution of raster data. With regards to vector data, as map scale moves from large scale to small scale, it has the effect of reducing our ability to be accurate and precise in measuring landscape features. The number of specific polygons, total length, and the area is reduced because it is much harder to accurately depict what is and is not a specific feature. You have to be much more general in your analysis and descriptions. It is also much easier to miss features altogether when viewing on a relatively small scale.

The images below help depict the effect of scale on vector data:

When it comes to raster data, our resolution is much worse at small scales and it forces you to be very general in your analysis for whatever purpose that may be.  If we generate a raster at a large scale, our precision and accuracy can be much greater.

The table below illustrates how resolution affects our interpretation of slope.  In general, the better the resolution, the better our ability to identify steep slopes and dynamic landscapes.

DEM Resolution	Average Slope (degrees)
1m	39.25
2m	38.98
5m	38.39
10m	37.47
30m	34.81
90m	30.31

The second part of our lab dealt with gerrymandering.  Gerrymandering is the redrawing of congressional districts in order to favor one party over another.  Gerrymandering generally increases divisions based on wealth and race.  The effects of gerrymandering can be measured mathematically using the Polsby-Popper score where a score closer to one indicates a more compact district shape.  Districts with a very low Polsby-Popper score indicate that it is drawn with purposes that are not impartial.  Below is an image of the district in the contiguous 48 states with the lowest Polsby-Popper score:

As you can see from the image, this district (congressional district 12) makes absolutely no sense in terms of how you might imagine a district if it were drawn to include an impartial representation.  There is clearly a motive behind drawing north Charlotte, and the interstate to Greensboro and Winstom-Salem.  One must question the motives behind any political actors who draw such a district.