How to Read a Congressional District Map

A congressional district map shows the boundary of the area that elects one member of the U.S. House. The lines can look arbitrary, but almost every feature on the map is there for a reason. Once you know what the shapes are doing, the map becomes readable.

Start with what the boundary means

Everyone inside the line is represented by the same House member. Everyone outside it is not, even if they live a block away. Districts are drawn to hold roughly equal population, currently about 760,000 people each, which is why a district covering a dense city can be physically tiny while a rural district covers most of a state.

Look at how counties are treated

Mapmakers often try to keep counties, cities, and towns whole, because splitting them makes government messier. When you see a county cut into two or three pieces, that is worth noticing. Sometimes the split is unavoidable, because the county has more people than one district can hold. A large county will always be divided. When a small county is split, it is more likely a deliberate choice.

Compactness is a clue, not a verdict

A district that is roughly round or square is called compact. A district with long arms, narrow connectors, or pieces that barely touch is not. Odd shapes get attention because they can be a sign of gerrymandering, but shape alone does not prove intent. Rivers, mountains, coastlines, and state borders all force irregular shapes, and so do rules requiring districts to keep certain communities together.

The useful question is whether the shape is explained by geography or by something else. A district that follows a river valley makes sense. A district that reaches 60 miles to pick up two neighborhoods and skips everything in between usually does not.

Watch for the two classic techniques

Packing puts as many of one group as possible into a single district, so their votes pile up in a race that was already decided. Cracking splits a group across several districts so they are a minority in each. On a map, packing tends to look like one oddly stuffed district, and cracking tends to look like a city sliced into wedges that each reach out into different suburbs. See packing and cracking for detail.

Check when the map was drawn

Maps are normally redrawn once every ten years after the census, but they can change in between when a court orders it or a legislature chooses to redraw. A map you find online may be out of date. See how congressional redistricting works and mid-decade redistricting explained.

Find your own district on a map

Every district page on this site includes an interactive boundary map drawn from U.S. Census Bureau data, along with the counties and largest cities the district covers. Use the lookup on the home page to find your district, or start from Browse Districts or the States page.