The U.S. Supreme Court this week is hearing arguments in a challenge to Maryland's congressional map, which is often held up as a textbook example of partisan gerrymandering.

For a sense of the extent of the Democrat-drawn gerrymander, consider this: In 2016, Republican candidates won 37 percent of the statewide two-party vote for U.S. House seats. But because of the way Democrats drew district boundaries after the 2010 Census, that translated to just one of the state's eight House seats.


To understand how Democrats pulled this off, we need to take a close look at the map. Here's what Maryland's congressional districts look like. I've used a high-contrast color scheme to help distinguish the serpentine boundaries clustered in the middle of the state.


On the basis of a simple visual inspection, the boundaries are something of a mess, following no discernible rhyme or reason. The districts are among the least geographically compact in the nation, which is often a telltale sign that partisan shenanigans are afoot.

But to fully understand the genius of Maryland Democrats' gerrymander, we need to impose the district boundaries over precinct-level 2016 presidential election results, so we can we can see how the borders interact with the state's partisan geography. I've done that at the state level below, using a map of precinct-level returns compiled by Ryne Rohla of Washington State University.


This is — not terribly useful, given the extreme convolutions of the district boundaries in the middle of the state. So let's take a look at a number of individual districts for a clearer picture. We'll start with the 6th District, in the western part of the state, which is the subject of this week's Supreme Court case.


The plaintiffs in the case, Benisek v. Lamone, allege that when Democrats created this district after the 2010 Census, their intent was to literally draw Republican incumbent Roscoe Bartlett off the map, creating another safe Democratic seat. The shape of the map suggests Democrats did this by creating an appendage in the southeast section of the district that captures a large chunk of Democratic voters in Frederick and an even larger number of Democrats in the northwest Washington suburbs.

Those two Democratic strongholds offset the Republican strength in all of western Maryland, creating a district that Democrat John Delaney won with a comfortable 56 percent of the vote in 2016.

As it turns out, most of the state's districts appear to have been drawn with the same general strategy in mind: to use liberal voters from the Washington metro area to offset conservative strength elsewhere. Here, for instance, are the 4th and 8th districts, both won by Democrats with more than 60 percent of the vote in 2016.


The 8th District contains much of the red country around Frederick that you might naturally assume would fit in more with the western part of the state. Instead, it shoots a narrow tentacle — no wider than a couple thousand feet at one point — down into liberal Montgomery County to capture the Democratic strongholds of the northern Washington suburbs.

The 4th district plays a similar trick, pairing Washington's eastern suburbs with red country outside Annapolis. It's held together at one point by the width of an aquatics center and the Potomac Curling Club. Ditto for the 5th District, which offsets much of Republican-leaning Southern Maryland with Democratic voters around Washington.

No account of Maryland's congressional districts would be complete without a stop in the 3rd District, which, following the redrawing of North Carolina's districts in 2016, now holds the dubious title of least compact district in the nation.


It's been called a “crazy quilt.” A “blood spatter from a crime scene.” A “broken-winged pterodactyl, lying prostrate across the center of the state.” At one point, the district is contiguous only by virtue of a swim across a tendril of the Chesapeake Bay. At another, it narrows down to the width of a block and a half in northeast Baltimore.

Writing for the New Republic in 2012, Jeff Guo drove across the district on Election Day 2012, “trying to find what its voters, fused together by partisan politics, had in common.” He didn't have much luck.

Republicans often defend their own gerrymanders by pointing out that partisan geography — the tendency of Democrats to cluster together in large cities — makes it easy to pack them away in a small number of districts, drawing maps that are advantageous to the GOP. But Maryland is an example of how partisan geography can cut both ways: Mapmakers can divvy up an urban area's Democratic voters among multiple districts, offsetting Republican power everywhere else.

These partisan incentives could be eliminated — or at least greatly reduced — by taking redistricting power out of the hands of state legislatures and letting nonpartisan, independent commissions draw the lines instead. That's how districts are drawn in states such as California and Arizona.

The Supreme Court's ruling in the Maryland case could influence whether more states follow suit before the 2020 redistricting cycle begins.

Correction: An earlier version of this story misidentified an appendage of the 6th congressional district. It extends from the southeast corner of the district, not the southwest.