Imagine that political opinion can be represented accurately and uniformly in 1 dimension. The white line at the bottom is that axis. The coloured dots (which you can drag) are individual voters with their preferences. The white dot is the status quo. Each dot's corresponding line covers the area on the axis they would prefer to the status quo.
What you'll notice is Black's median voter theorem: The white rectangle always surrounds the largest area of majority support/preference over the status quo, and this is ALWAYS equal to the area that the median voter prefers to the status quo.
