DRA 2020
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DRA 2020

Building Your District Map

This article will walk you through building a state district map from a blank map. You’ve already selected a state and number of districts. Now you’re looking at something like this.

Your goal, at the very least, is to assign all the precincts to districts so that each district has about the same population, and to make sure each district is contiguous (all precincts are connected). As you work with your map, it will always be saved in the cloud.

Painting

You assign precincts to districts by painting the map.

Use the radio buttons in the District Selector (left panel) to select which district to paint.

Click the Paint Brush (top bar) to toggle to Paint Mode. You can paint counties or precincts, and you can adjust the brush size for painting precincts. You can also double-click on the map top toggle Paint Mode. Click the Eraser to erase and Pan (hand) to exit Paint Mode.

In Paint Mode, click on the map to assign precincts or counties to the selected district. As you move the mouse over the map, the shaded area is what will be painted when you click. You can hold the left mouse button down and sweep to paint.

You can also drag out a box and paint everything in it. Hold Ctrl (Windows) or Command (Mac) down, then hold the left mouse button down, drag out a box and release the mouse button.

Controls

Various controls and tools can help you as you decide how to paint the map. The Colors section (lower left panel) let’s you view the map colored by Partisan Lean or various demographics. The following image shows all precincts colored by Partisan Lean, using discreet bands. A gradient color option is available if you prefer.

The next image shows the map colored by an All Minorities gradient. If you check the Districts checkbox together with Partisan Lean or one of the demographics choices, precincts that are assigned to a district will show as that district’s color; only unassigned precincts will show as the Partisan Lean or demographic color.

The Details panel (right panel) shows the dataset details of the precinct or county your mouse is hovering over. In the above image the data for precinct Solomon 1 is shown.

The Overlays section in the left panel has options to show the background map, county lines, district labels and more, and an Opacity slider.

Strategies

Your strategy as you paint your map can make a big difference.

  • Think about what your goals are. Are you trying to keep certain demographic groups together? Are you trying to make a partisan map? Are you going for compactness or competitiveness or proportionality? Do you want to minimize changes from the current map?
  • Painting counties can be a good place to start, especially for sparsely populated areas. You can always erase or paint over previously painted precincts. Use the precinct’s brush size to paint faster.
  • If you have specific groups, such as minorities, that you need to keep together in a district, it’s a good idea to start there.
  • Having a rough idea of where your districts should be centered can help.
  • Once you start painting, don’t try to make the first district perfect without painting other districts. Instead, make a rough cut of each and then refine; you’ll always have to tinker around the edges to meet your target population goals.

End Game

As you get to the last few precincts, you’ll likely be looking at the population and deviation (from the target population) columns, tinkering to get as close to the target as possible. Sometimes it’s difficult to locate a few small precincts that didn’t get painted, or there may be mis-painted precincts that make your districts non-contiguous.

The tools Find Unassigned Precincts, which will find and zoom to unassigned precincts, and Find Non-contiguous, which will find and zoom to disconnected portions of each district, will help you find those problem areas.

Click Statistics to see information about population, partisanship, demographics and more, for the districts you’ve created. This can help you get closer to your goals for the map. In the example below, you can see that four districts have unequal population and two are not contiguous. In addition, three districts have over 40% minority population.

Click Analytics to see your districts measured along five dimensions. This article has more information on those measures.

Your map is always saved in the cloud. When you’re done, you can Publish it, so everyone on DRA 2020 can see it. You can Share it with friends or colleagues as well.

Good luck!

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Dave Bradlee

Software Engineer. Creator of Dave’s Redistricting App (2010) and co-author of DRA 2020.