GIS 5935 Module 3.1: Scale Effect and Spatial Data Aggregation

     An important consideration in mapping to take into account is scale. The larger the scale value, the more detailed a map may be (showing a smaller area). For example, if we were to make a map of airports with airports represented as points (vector data) and we zoomed in significantly, we would be able to see many more details (polygon features indicating building, lines indicating runways). As a note, vector data consists of points, lines, and polygons.

    Raster data, on the other hand, is comprised of cells. The smaller the cells, the more details/higher resolution. The bigger the cells, the lower the resolution. The level of detail relates to the processing time of the data cells, so the higher the resolution, the more processing time is necessary.

    Gerrymandering is manipulation of districts to give an advantage to one political party over another. One way to determine if a district is undergoing gerrymandering is to determine the  “compactness” of an area – one way to do so is to calculate the Polsby-Popper score using the formula:

Polsby-Popper Score =    4×π×Area
                                           Perimeter^2

The closer to (1) the resulting score is, the more "compact" it is, indicating no/little gerrymandering occurring. The worst “offender” in this lab that fails to have district ‘compactness’ is Congressional District 12 of North Carolina, USA with the Polsby-Popper score of 0.029-- below is an image outlining this District in blue: 


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