Draw districts by population size
The United States Constitution requires a count of the U.S. population every 10 years. Results from the census impact how many seats in the House of Representatives are reapportioned to each state. Each state legislature or redistricting commission has its own process for redistricting, but every state must comply with the federal constitutional requirements related to population and anti-discrimination. These requirements were intended to make the districts easy to identify and understand and to ensure fairness and consistency.
Examples of federal and constitutional requirements include the Apportionment Clause of Article I, Section 2, which requires that all districts need to be as equal in population as possible. Another important piece of legislation was the Voting Rights Act of 1965, which prohibits any plans or practices that intentionally or inadvertently result in the denial of any citizen the right to vote on the basis of race.
States can adopt their own redistricting criteria, or principles, for drawing the plans. Principles, or criteria, may be found in state constitutions or statutes or may be adopted by the legislature, chamber, or committee. For instance, the state of Maryland requires the compactness of districts and that lines should be drawn with consideration to existing natural and political boundaries. (Md. Const. art. III, §§ 3-5). Some states, such as Colorado, specify the degree to which their population deviation per district may range, restricting districts from having a population deviation above 5 percent (Colo. Const. Art. V, § 46).
To help you draw new districts, you'll use Esri Redistricting, also known as Redistricting Online, a web-based solution that enables governments, advocates, and citizens to draft, edit, and share regulation-compliant redistricting plans.
Learn more about how to use Esri Redistricting.
You'll open the app, add census data, and draw districts based on population.
Open a plan
Maryland, one of the United States' 13 original colonies, is a diverse state stretching from the Atlantic Ocean to the Appalachian Mountains. The Old Line State has approximately 6 million residents; it ranks nineteenth in U.S. population despite ranking forty-second in size. Its relatively densely packed population has eight elected officials in the United States House of Representatives. For this lesson exercise, you'll map seven districts.
First, you'll start Esri Redistricting and start a new redistricting plan.
- Sign in to your ArcGIS Online organizational account.
If you don't have an organizational account, you can sign up for a free Learn ArcGIS organization trial account which includes access to Esri Redistricting.
- At the top of the page, click the app launcher button.
- Click Esri Redistricting.
If Esri Redistricting does not open, ensure your browser language is set to English.
- Click the Sign in button. If necessary, in the Licensing Agreement, click Agree to continue.
Esri Redistricting opens with the Open Plan window open.
- In the Open Plan window, click Create Plan.
The New Plan window appears. From here, you'll create seven districts in the state of Maryland.
- In the New Plan window, set the following parameters:
- Verify that District Caption is set to District.
- For Number of Districts, type 7.
- For Maximum Deviation, accept the default of 10 percent.
- For Census Year, choose 2010.
- Under Select source geography, expand States and choose Maryland_2010.
- Verify that Select data hierarchy is set to County-Tract-Block Group-Block.
- Click Next.
The next window has options to modify the colors of the districts. You will accept the default settings.
- Click Next.
The next window has options to assign demographics. Redistricting to equitably balance several demographic groups within the same district can become a time-consuming and complex process. For brevity, in this lesson, you will only consider the distribution of the Non-Hispanic White and Non-Hispanic Black demographic groups.
- Under Select demographics to display, in the Name column, expand Standard.
Race and ethnicity categories are listed with a more detailed description.
The United States Census Bureau must adhere to the 1997 Office of Management and Budget (OMB) standards for race and ethnicity. Esri Redistricting uses the same language as the United States Census Bureau.
- For Name WHITENH and BLACKNH, check the Sum column.
The NH in WHITENH and BLACKNH stands for Non-Hispanic.
- Click Done.
The Save Plan window appears. You can opt to save the plan during plan creation or at a later point. For this exercise, you'll save the plan later.
- Click Cancel.
A one-color map of Maryland appears because all seven districts haven't yet been assigned. New colors will be added to the map as voters are assigned to districts.
Below the map is the District Window which displays the districts in your current plan, the symbology for each district, and the population count for each district and demographics per district. You'll keep the districts at the county level, and target populations between 600,000 and 1,000,000, for the ease of training. Having the target population anchored in the District Window will give you a guidepost for each district's population goal.
- On the ribbon, click the View tab, and in the Districts group, check Show Target Values.
The TARGET column is now visible in the District Window, showing the target mean of 824,793 residents per district. That number represents the ideal of creating seven equally balanced congressional districts among Maryland's 24 counties (the city of Baltimore, a county equivalent, became independent after splitting from Baltimore County in 1851). At the county level, it's impossible to place equal populations in each district; such an effort would require street-by-street redistricting.
Now that you have identified your population targets, you'll spread the populations among seven districts you will create in the next step.
In this section, you will use the Esri Redistricting workflow to draw seven districts and ensure the population distribution between them is relatively equal.
- On the ribbon, click the Learn tab and review its contents.
The Learn tab contents discuss the Esri Redistricting workflow and provide a quick tour and answers to frequently asked questions.
- Click the Create tab.
The Redistricting group allows you to select geography by points, rectangles, polygons, and polylines. You'll use the Select geography tool and select by point. Because you previously chose the county selection level, each time you click, the entire county within the district you're creating is included.
- In the Redistricting group, click the Select geography by picking them tool to activate it.
- In the Redistricting group, for District, choose District 1.
District 1 is now set as the active district you are editing.
Alternatively, in the District Window, you can click any row to activate that district.
- On the View tab, in the District Display group, check Show District Field.
By checking the box for Show District Field, you will see the accumulated population for the district you're creating on the map.
- Starting with Maryland's western border, click each county as you move your pointer east.
As you click, the population of District 1 is totaled. Stop when your population covers most of the panhandle of Maryland and the population of the district equals 653,133. The colors of your districts may vary.
To make a change, on the Create tab, in the Redistricting group, click the Undo and Redo buttons.
- On the Create tab, in the Redistricting group, for District, choose District 2 and in the map, click the county immediately northwest of Washington, D.C. (It has a population of 971,777.)
- Set the active district to District 3 and click the city of Baltimore.
Counties are added to a district when you click them. To change which counties belong to which districts, you must first activate the district by clicking its row in the District Window or choosing it from the District drop-down menu. You can then click the county you want to move into the district you just activated.
- For the remaining four districts, click each row of the District Window and click the map to populate that district.
Remember, you're aiming for each district to number between 600,000 and 1,000,000 residents.
- For the remaining four districts, Districts 4 through 7, use what you have learned to activate each district and click the counties on the map to populate the districts, aiming for 600,000 to 1,000,000 residents per district.
Use the navigation buttons in the upper left corner of the map, or in the Tools group, if necessary, to pan and zoom. If you use those navigation buttons, you'll have to again click the Select geography button to resume your work.
When complete, your map shows the desired balance among the seven districts.
Save and name the plan
Now that you have a proposed redistricting map, you need to name and save it so you can share it later.
- At the top of Esri Redistricting, click the Save As button.
Alternatively, in the File menu, in the Plans group, you can click the Save As button.
- In the Save Plan window, set the following parameters:
- For Name, type First draft.
- For Description, type First draft of redistricting plan for seven congressional districts in Maryland.
- Click OK.
You've created a redistricting plan for Maryland. You balanced the districts to ensure equal population representation among the seven congressional districts. To learn more Create and edit plans.
Next, you'll download Maryland's 2012 Congressional District Plan and balance the districts by race and ethnicity data.
Edit and redraw district boundaries
Previously, you created a plan that balanced seven congressional districts based on Maryland's estimated 6 million residents. Next, you'll download a file named 111th Maryland Congressional District that reflects the state's current congressional boundaries. You'll save the plan under a new name and practice adjusting the boundaries for two districts.
Balancing districts to meet all the criteria required by a specific state’s constitution and the Voting Rights Act can be challenging and requires time and dedication. Every population has different needs, and diverse communities are distributed differently. Identifying the appropriate percentage of representation per district depends on the specific state, population distribution, and at times political decisions of a given redistricting body. For this lesson example, you will redraw the district lines for District 3 so the percentage of Black residents is between 40 and 50 percent.
To learn more about U.S. congressional redistricting and the impact of the Voting Rights Act, view American redistricting history.
Load and prepare a plan
You'll download a PLAN file, a file format used and recognized by Esri Redistricting.
- Download the 111th-maryland-congressional-district PLAN file and save it to a convenient location on your computer, such as your Desktop.
- If necessary, sign in to Esri Redistricting and on the File tab, in the Plans group, click Open.
- In the Open Plan window, click Open Local Plan and browse to where you saved the PLAN file locally on your computer.
- Open the 111th-maryland-congressional-district folder, click the 111th-maryland-congressional-districts.plan file, and click Open.
After the PLAN file loads, a map of Maryland's 2012 congressional districts appears.
Your map shows the eight congressional districts of Maryland during the 111th Congress.
- On the side of the map, click the gray arrow to expand the side panel and click the Contents tab to view the Contents pane.
The Contents pane contains several layers, including the Streets basemap.
You'll be working with the Districts layer, which contains data derived from the 111th-maryland-congressional-districts PLAN file you downloaded earlier. The US Congressional Districts 2011 layer obscures the Maryland_2010 layer, so you will turn it off.
- In the Contents pane, uncheck the US Congressional Districts 2011 layer.
To help you keep track of the district names, which districts are editable, and the population total for each district as you make adjustments, you will configure display settings on the View tab.
- On the ribbon, click the View tab, and in the District Display group, check Display Locks and Display Names. Confirm Show District Field is checked.
Every district should have diagonal lines indicating that the data in each district is locked and cannot be edited. The Lock column in the District Window indicates whether a district is locked and can be checked and unchecked to make specific districts editable or to lock them so they cannot be edited.
The plan is now configured and ready for editing the district boundaries.
Next, you'll save the plan.
- On the File tab, in the Plans group, click Save As.
- In the Save Plan window, set the following parameters:
- For Name, type Proposed Congressional Districts, followed by your initials.
- For Description, type First draft of a new District 3 in Maryland.
- Click OK.
The plan is saved under the new name, which is listed at the top of Esri Redistricting.
Next, you'll unlock District 3 and zoom to its location.
- Click the Create tab. In the Redistricting group, for District, choose District 3.
- Click Zoom to view the selected district.
The map zooms to District 3, which is the focus of the district you'll redraw. You may want to zoom in one level more. Your map colors may vary.
- Pan and zoom your map, if necessary, so District 3 is in the center. Click the Pan button in the Tools group or in the navigational tools on the left.
- To close the Contents pane, click the gray arrow.
The District Window shows how the populations, with deviations above and below 7,000 residents, were brought into balance after the 2010 United States Census.
To show these percentages, you will open the Demographics table and add percentages to the District Window reflecting the percentage of Non-Hispanic Black and White populations.
- On the Create tab, in the Statistics group, click the Demographics button.
- In the Demographics table, expand the Standard folder. In the Percent column, check WHITE NH and BLACKNH.
- Click OK.
The District Window adds columns showing percentages of Non-Hispanic Black and White populations.
District 3 currently has 55.5 percent Non-Hispanic Black residents.
Next, you'll adjust the district boundary between District 2 and 3 so the percentage of Non-Hispanic Black residents in District 3 is between 40 and 50 percent.
Adjust district populations
When it comes to drawing district lines for equal representation, it can be a complicated process because communities do not always fit into compact sections of a jurisdiction. An ideal district may be one that has just the right percentage of communities of color to elect a representative who can best represent the demographics of the district. However, the percentage of people of color cannot be too low, or else communities of color may be fragmented into several districts, potentially limiting those communities from voting for a candidate of their choice. If the percentage of people of color in a district is too high, each of their votes may not hold as much weight because the preferred candidate might win by an overwhelming margin. Determining a legally acceptable percentage of people of color within a district requires statistically analyzing election results to determine the degree of racially polarized voting, then drawing a district with a high enough percentage of people of color to elect a candidate of choice, using the results from the statistical analysis.
For this lesson, you will not conduct a statistical analysis, but it is worth acknowledging the work of drawing lines in an equitable manner is complex, but important. For this lesson, you will redraw the district boundary between District 3, which represents the greater Baltimore area and a historically Black community, and portions of District 2, which encompasses portions of Howard, Frederick, and Carroll counties, areas with a high concentration of White residents.
Next, you'll alternatively activate District 2 and District 3. With each, you will use the Select geographies by rectangle and Select geographies by polygon tools to transfer sections of one district to the other. As the district lines change, the District Window will update, indicating the demographic percentage for each district.
- In the District Window, in the Lock column, verify that all the boxes for each district are checked.
- Uncheck Lock for District 2 and District 3.
The diagonal lines reflecting locked data disappear for those two districts; however, only one district can be active at a time.
- On the Create tab, in the Redistricting group, verify that District 3 is active and click Select geographies by rectangle.
Select geographies by rectangle is useful for when you want to move bigger portions of a district; Select geographies by polygon (the button to its immediate right) is appropriate for smaller areas or fixing errors when you're redrawing lines.
- Zoom to the area where District 2 and District 3 share a boundary.
To maximize map space, you can minimize the District Window by dragging down its handle; ensure that District 2 and District 3 remain visible.
- Using the Select geographies by rectangle tool, and with District 3 active, draw a rectangle around the Eldersburg area.
Sections of District 2 transfer to District 3, and the field values in the District Window update.
Your map and resulting table results may not appear exactly as the example image in this lesson.
In the District Window, notice the column for TOTAL. You want to ensure that for both District 2 and District 3, the population is maintained around 720,000.
For the BLACKNH_P column, representing the percentage of Non-Hispanic Black population, you will aim to redraw the boundaries so the value for District 3 is between 40 and 50 percent.
Next, you'll activate District 2 and use the Select geographies by polygon tool to make incremental changes.
- In the Redistricting group, for District, choose District 2.
- In a manner similar to changing the district for District 3, use the Select geographies by polygon tool to select a different area to bring into District 2.
- Using the two selection tools, move areas between District 2 and District 3 until BLACKNH_P is between 40 percent and 50 percent and TOTAL is between 728,000 and 714,000 residents. Keep the District Window open while you transfer areas.
When transferring geographies between districts, you may inadvertently create islands and pockets of areas that didn't transfer to the district you intended. This results from the underlying geography—such as blocks, block groups or tracts—you may have missed with your geography selection tool. These missed areas could also stem from geographies being linked to locked districts. To avoid creating such islands and pockets, zoom in to the Block or Block Group level when you make your selections. You may also change the selection level in the Selection Level slider.
When complete, your map may resemble the example map. Your map colors may vary.
The District Window should show that the total populations of District 2 and District 3 fall between 714,000 and 728,000 and the Non-Hispanic Black population of District 3 is between 40 percent and 50 percent.
- Check the boxes to lock District 2 and District 3.
- Save the plan.
You have successfully drafted a proposal for District 2 and District 3 in Maryland.
Test your plan
Previously, you redrew the district boundaries between District 2 and District 3 in Maryland. Next, you'll use the tools in the Analysis group to run a battery of tests about those two districts. If your plan fails, you'll fix the errors.
Run the Check Integrity test
Congressional districts must be compact, contiguous, and equal. To help, Esri Redistricting includes tools that can test whether your plans meet those requirements.
- Open your plan.
- Click the Review tab, and in the Analysis group, click Check Integrity.
Esri Redistricting produces a report of its integrity tests. In this case, your map did not pass the Connectivity Check because all districts are required to be contiguous.
- In the Integrity Tests window, for Connectivity Check, click Details.
The Discontiguous Districts window appears.
This table means that while drawing, you created islands or pockets cut off from their districts. You'll fix this with the Select geographies by polygon tool.
The numbers in your Discontiguous Districts table may vary. Next you will resolve these isolated areas identified by the check.
- In the District Window, unlock District 2 and District 3 and fix those isolated areas.
- Drag the
Discontiguous Districts window to the side and zoom in to those districts and pan the boundaries until you locate those isolated areas.
- Click the Create tab. With the Select geographies by polygon tool, draw small polygons around each island or group of islands. You may have to alternate the active district to move those islands to the desired district.
- In the Discontiguous Districts window, click Refresh to the Check Integrity test.
If you find more islands, you can also use the Next Part button in the Discontiguous Districts table to find them.
- In the Discontiguous Districts table, click any district and click Next Part.
The first image you see outlined in yellow is likely the largest part of the active district. You'll join the isolated island to the area represented by the larger image so you have one contiguous district. The map you downloaded may have contained several errors involving districts other than 2 and 3, so you'll also have to fix those errors before your map can pass the integrity test. Many of these isolated islands involve relatively few people; transferring these won't significantly affect populations in the District Window. Districts must be active and unlocked before a population can be transferred; this means you must alternatively work with the active district and select geographies tools to complete those moves.
Use the Select geographies by polygon tool to select the misaligned districts. If you make a mistake, click the Undo button to reverse the error.
- Using the Discontiguous Districts table, click the Next Part button to find and fix each isolated area.
- When the Discontiguous Districts table is empty, close the window to rerun the Integrity Tests.
It's possible that you created more violations during your reconfiguration. If necessary, click Details and address each issue as needed. The tests will fail until all districts are contiguous.
A results box with six green check marks means you have successfully completed this battery of tests.
- Lock all the districts in the District Window.
- Close all the tables and save your plan.
Run the Compactness test
Compactness is one of the redistricting criteria analysts consider when redrawing political boundaries. Most states require districts to be compact; unfortunately, many states don't define or detail their own compactness standards, so there's no one definition for compactness.
However, over time, scholars have produced more than 30 mathematical formulas determining compactness. Esri Redistricting uses seven of those formulas, which include the Reock Test (compares the ratio of district area to a circle), Perimeter (calculates the perimeter and reports results in miles), and Polsby-Popper (compares the district perimeter to a circle). Each test has its own scoring system. Each formula has its advantages and disadvantages.
In Esri Redistricting, you have one button that will run a test listing a variety of compactness scores.
- Click the Review tab, if necessary.
- In the Analysis group, click Compactness Tests.
The Compactness Tests table lists the measurements of each district. The Holes column on the right should have a zero in each row because you have already eliminated those islands during the Check Integrity test.
The information contained in the Compactness Tests table could be valuable information depending on the compactness standard of each state. If you were to redraw the lines, you would see a different listing of measurements.
- Close the table.
- Save the project.
You've tested the proposed plan against the Check Integrity and Compactness Tests tools. With Check Integrity, you fixed the errors listed in the results table. With Compactness Tests, you viewed a table listing seven mathematical formulas as applied to your proposed map. These checks help you ensure your plan is in line and credible with the important criteria that review boards or possible court challenges will need to consider before passing your plan proposal. To learn more, see Analyze and review redistricting plans.
Publish your plan as a web map
Previously, you successfully tested your congressional plan. Next, you'll publish your map so fellow analysts can review your work. You'll share your plan as a web map within your ArcGIS organization, which allows you to keep your redistricting plan internal until you're ready to release your plan to the public.
Share your work
Now that you have a redistricting plan, you want your peers to see it first so you can collect their feedback.
- Open your plan.
- Click the Share tab.
In the Community group, you have the options to publish a map package, publish KML, or publish a feature layer. The map package allows you to share through ArcMap. KML gives you the option of publishing to ArcMap or ArcGIS Online. For this lesson, you'll use Publish Feature Layer, which gives users more flexibility as a feature service by enabling them to edit in ArcGIS Online.
- In the Community group, click Publish Feature Layer.
- In the ArcGIS Online - Feature Service window, click Next.
At this point, you're not ready to release your map to the public. It still requires staff review, so you'll keep it internal. When you're ready to release it to the public, you'll use this same workflow, but you'll check the Everyone (public) box.
- Save to your folder and click Next.
- In the next window, set the following parameters:
- In the Use Constraints box, type Confidential, internal use only until ready for public release.
- In the Summary box, type Staff research into proposed redistricting plans for Maryland.
- Click Publish.
After a few moments, a window appears, indicating the feature service was successfully published.
- In the window, click the link.
If you click OK, you'll need to sign in to your ArcGIS Online account and navigate the map.
The link opens to the details page of your feature layer.
- On the item details page, click Open in Map Viewer.
Depending on your organizational and user settings, you may have opened Map Viewer Classic. ArcGIS Online offers two map viewers for viewing, using, and creating maps. For more information on the map viewers available and which to use, please see this FAQ.
Your feature layer opens in ArcGIS Online.
- Zoom in and click anywhere within District 3.
The pop-up appears and shows the demographic percentages as well as the overall population count.
At this point, your ArcGIS Online map is passive. To create a new map based on this information, you will need to save it as your own map so you can edit the layers. Consider exploring the Learn ArcGIS lesson Get started with ArcGIS Online to learn more about how to configure map appearance and pop-ups as well as creating and sharing maps.
You can set up your web map so that your fellow staffers can create their own maps and share them within your organization. They can also make presentations they can discuss and circulate internally. Once a final map is decided, you can use the portal to release your proposed map to the public for its review and comment well before your elected officials vote to accept or reject your map. To learn more, see Collaborate with other users and groups using Esri Redistricting.
In this lesson, you created a redistricting map based on 2010 United States Census data. You also edited the district boundary between two districts. Your plan successfully completed six integrity tests, which increases its chances of being accepted by your elected officials and, if necessary, surviving a court challenge. Finally, you shared your plan with fellow staff members through your portal.
Esri Redistricting can be used to redraw state and congressional districts, however, its tools would work just as well with the type of districts that don't receive as much attention, such as trash, fire, school, or police.
If you are interested in learning more about using GIS tools for redistricting, check out the Learn ArcGIS lesson Analyze impacts of congressional redistricting with ArcGIS Insights to explore the demographics of various redistricting plan proposals and understand their potential impact.
You can find more lessons in the Learn ArcGIS Lesson Gallery.