Creating a District Map

Dave Bradlee
Apr 20 · 5 min read

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

You’re goal, at the very least, is to assign population to the districts so that each district has close to the same population, and to make sure each district is cohesive (all blocks are connected). As you work with your map, it will always be saved in the cloud.


Coloring

The way you assign population to your districts is to color the map.

  • Select the district you want to color using the radio buttons in the left most panel.

Controls

Let’s look at some of the controls and tools that can help you as you decide how to color the map:

  • The top bar has the Show section. By default District Colors is checked, which will show the district color of each BG/VT that you have colored.
  • The last checkbox Demographic Colors (All Groups) shows each BG/VT by its demographics. The associated dropdown can be used to show colors by a specific demographic.
  • When you hover over a color unit, a popup toward the lower left shows the data for that color unit. The position of the hover can be adjusted: click on Show (on the top bar) and change to Adjust. Click the check box to show an arrow control to adjust the position.

Import Existing Maps

One way to start a map is by importing an existing map.

  • Some states publish block mappings (aka block equivalency) of the maps they drew in 2011, usually as CSV listing each census block id and the district to which it was assigned. After you have created a blank map, you can click the Gear icon (upper right) to take you back to Map Set Up and Auto Color. From there choose the file and click Apply, which will color the map according to that information. [Note: this currently works only for 2016 Block Group datasource.]

Strategies

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

  • Think about what your goals are. Are you trying to keep certain groups together? Are you trying to make a partisan map? Are you going for compactness or competetiveness or proportionality? Do you want to minimize change from the current map?

End Game

As you get to the last blocks to color, you’ll likely be looking at the population and deviation columns, tinkering to get as close to the target as possible. There are a few other things you should do as well.

  • Check cohesiveness and for unassigned blocks. To do this, click Show, and change the dropdown to Check, which will show two checkboxes. Find Unassigned will zoom in to where any unassigned blocks are. Find non-cohesive will zoom in to any disconnected portions of a district.
  • Look at the Analytics by clicking Analyze Map. This will give the demographic breakdown, partisan makeup and compactness of the districts. [More analytics are under development.]

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 a few friends or colleagues. You can take screen shots of it and post them on your blog. You can also Export it as a .json or .csv file.

Good luck!

DRA 2020

Dave’s Redistricting App

Dave Bradlee

Written by

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

DRA 2020

DRA 2020

Dave’s Redistricting App

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