Spread of information
With the elections still not over, there have been a lot of recounts and anxiety as to which state would become what color. Looking closely at each state though, there are counties that are clearly divided. And then there are regions in which there is a more moderate view. This can be explained by the way information is spread and how people generally do what everyone else around them does.
https://www.cnn.com/election/2018/results/georgia/governor
In this link for example, when you look at the map, you can see regions in which either blue or red is very deeply colored. However, surrounding the deep blue, are lighter blues for they are surrounded by reds. This is because the people around them are both blue and red while the people in the center of that group in the map have blues around them. There is no incentive for them to switch to red. So, people tend to have the same views and mindsets as the people around them. This also resonates with connections formed. If some node is connected to A (being a B) and has 3 connections to A and none that are B, it will flip to A demonstrating how people tend to be like-minded with those around them.