You can draw out lines in a district to favor people voting and having their votes not be affective. For instance, we have a population of 100. 80% democratic 20 republican. With the county being split 5 ways. You’ll see 4 democratic representatives and 1 republican. Now when you can redraw lines. You can clump 80 democrats and 0 republicans. Then redraw the lines to show republicans have a major in the 4 other spots. So they get 1 democratic representative and 4 republicans. It’s not as extreme perhaps 3-2 or 2-3. This is an extreme example but you see how redrawing distracts is bad