Special Topics - Mod 3 - Lab 6 - Aggregation and Scale

 Hello and Welcome back! 

My how time has flown. It has almost been 8 weeks, and 6 different labs. There have been so many topics covered in this short time, and here we are hitting on a combination of new and reinforcing of previous once more. 

This final module for Special Topics focuses on how scale and resolution affect vector and raster data respectfully. The overall theme there is on observing some effects with the Modifiable Area Unit Problem (MAUP). That refers to the issue that comes up when reviewing spatial analysis results of a data set across varying scales or changes in size, shape, or boundary of some spatial unit. This leads to the possibility of interpreting the same dataset multiple ways depending on the enumeration unit used. Finally we end that discussion with the ultimate form of boundary manipulation used for political boundaries, gerrymandering. 

A little back to the basics, Scale refers to the overall detail present in a map or scene. Large scale references a higher amount of detail over a smaller geographic area. Conversely small scale is a much broader area with less detain. The larger the scale the more detail we have, the more data and true surface information maintained. 

Resolution for raster data refers to the size of each pixel. The size of the pixel affects the level of detail. Generally put, an object must be larger than the minimum resolution (pixel size) to be distinguishable in a raster image. Again, high resolution has more detail but usually represents a smaller ground area. This does come with the tradeoff of needing much more processing power and digital storage capacity. 

Gerrymandering on the other hand refers to the adjustment of electoral district boundaries to favor a particular party. Its overall goal is to influence election outcomes in that particular district, by having the majority demographic grouped together. There are numerous ways to try to determine the degree to which a district is or isnt gerrymandered. for this module I took two different approaches. I calculated the Polsby-Popper and Reock Compactness scores. They both have a unique formula relating to the area and perimeter length of a congressional district. 

Polsby Popper = 4π × Area​ / Perimeter²

Reock = Area of District / Area of the Smallest Enclosing Circle

These both focus on comparing the area or perimeter of the district to a similarly sized or enclosed circle. Polsby-Popper looks at a circle of the same perimeter size, and Reock looks at the smallest circle that can hold the district area.

Computationally I was able to do all of the Polsby Popper calculations within a modified Congressional District feature class. The primary modification was to only include the continental United States. The Reock computation involved creating a new feature layer by use of the Minimum Bounding Geometry tool. This tool took all of the data from the District feature and created the smallest circle corresponding to the size of the representative district polygon. From there, the circles area was divided into the district area for comparison. The image below shows some of the "worst offenders" for the Polsby Popper Score. 

This look at the South Eastern United States has 3 different Red areas were were the Top 3 worst scores. 

Here is a zoomed in look at the #3 offender, specifically highlighted because it falls within our very own Florida. You can see that this district covers an area from Orlando to Jacksonville. It also doesnt take a direct path to get there between the two. While the coastal districts are a little more regularly shaped, they are not without impact from Gerrymandering. They too likely have the opposite demographic indicators of this particularly highlighted district. 

Ultimately Gerrymandering is a deliberate manipulation of the political system, but it can be measured and analyzed, thats what the above serves to do, by having applied the same calculation to every district, then excerpting some of the lowest scores. 

It has been a wonderful class, and doesnt feel like this ones concluding. What does that ultimately mean? That even more learning is to come as we jump into the true masters portion of the courseware. Thank you for joining me. 

v/r

Brandon