The picture above shows part of the line dividing Nevada’s 1st (north) and 3rd (south) congressional districts. The line follows East Russell Road for this stretch almost perfectly, but juts upward for a block and comes back down. What is so special about the 13 residents that live there that warrants a change in an otherwise smooth line? Why not the block next to it? Why a jut at all?
It’s worth noting that that deviation from the line represents a single Census block, which is the smallest unit of geography that the Census reports population counts for. What this means for mapmakers is that the lines of a state’s Census blocks represent the possible lines for their districts: they can’t split a block, since they won’t know how many people are in either division.