Here is an example what gerrymandering looks like. It is an anti-democratic practice that is used to guarantee safe seats for Congressmen. It is practiced by both parties.
When we say that in America there is “one man, one vote,” gerrymandering compromises this bedrock principle of our democratic republic. In some circumstances gerrymandering is used to guarantee that minorities will have a voice in Congress. The goal might be noble, but the practice works against the necessary competition of ideas in the marketplace of ideas.
All Congressional districts include the same number of voters, but gerrymandering ends up, as well, excluding equal representation based upon the one man/one vote principle.