The factor that plays a signficant role in the shifting of both voting patterns and district boundaries is population.
Explanation:
In the United States, district boundaries and voting patterns are largely dependent on population. This is one reason why the national census carried out in the United States every 10 years is so important. The information from the Census is used to delegate federal money for government programs, it is used by the Department of Education for school district information, and it is also the basis for drawing up congressional district boundaries and for assessing voting patterns. In most states, the district boundaries are decided by the state legislature and both chambers have to approve the boundary plans in the majority. In some states, the governor has the power to veto this decision, but in others, he does not. In recent years there have been criticisms of this system because it can be subject to political manipulation where through gerrymandering a party tries to divide up a district, for example. This happens when say a poor neighborhood that wants to vote Democrat is split between two neighborhoods that vote Republican so that the Republican wins both seats more easily.
