Why is gerrymandering effective?

The gerrymandering is effective in two ways. One is to gain political advantage and the other is to influence voting choices.

The practice of gerrymandering is a way of manipulating political boundaries to create politically advantaged voting districts. It results in extremely mis-shapen political districts that can be used to manipulate the elective process. The purpose is to minimize the effect of opponents' votes and maximize the effect of supporters' votes.