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, 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.
Open a plan
Maryland, one of the United States' 13 original states, is a diverse state stretching from the Atlantic Ocean to the Appalachian Mountains. It 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 tutorial, you'll map seven districts.
First, you'll start Esri Redistricting and start a new redistricting plan.
- Sign in to your ArcGIS organizational account.
If you don't have an organizational account, see options for software access.
- 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 Sign in. If necessary, in the Licensing Agreement, click Agree to continue.
Esri Redistricting opens and displays the Open Plan window.
- 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 10.0 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'll 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 the purposes of this tutorial, you'll 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 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 tutorial, 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. 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've identified your population targets, you'll 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.
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 Show District Field, you'll see the accumulated population for the district you're creating on the map.
- Starting with Maryland's western border, click the first five counties as you move your pointer east.
As you click, the population of District 1 is totaled. The first five counties cover most of the panhandle of Maryland; the population of the district equals 653,133. The colors of your districts may differ from the example images.
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. On the map, click the county immediately northwest of Washington, D.C., where Germantown is located.
This county 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.
- Create the remaining districts using the following instructions (you may consult the map in the next step if you have difficulty):
- For District 4, click the county to the north of the city of Baltimore. (It has a population of 805,029.)
- For District 5, click the 10 counties on the eastern part of the state, starting with the county to the east of District 4. (The 10 counties have a combined population of 694,052.)
- For District 6, click the county directly south of the city of Baltimore, then the county directly south of that county. Then, click the two southernmost counties in the state that aren't already assigned to a district. (The 4 counties have a combined population of 878,095.)
- For District 7, click the county directly east of Washington, D.C. (It has a population of 863,420.)
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.
One county remains unassigned. You're aiming for each district to be as close as possible to the target value of 824,793. You'll add the last unassigned county to the first district to bring it closer to the target.
- For District 1, click the unassigned county east of District 2.
Now, your map shows the desired balance among the seven districts.
Save and name the plan
Now that you have a proposed redistricting map, you'll name and save it so you can share it later.
- At the top of Esri Redistricting, click the Save the plan using a different name 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, see 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 tutorial, you'll 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 zip file. Extract the file to a convenient location on your computer, such as your Desktop.
- In Esri Redistricting, click the File tab. In the Plans group, click Open.
- In the Open Plan window, click Open Local Plan and browse to the extracted folder.
- Open the 111th-maryland-congressional-district folder, click the 111th-maryland-congressional-districts.plan 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. There are several overlapping layers, so you'll look at the map contents and hide the layers you're not using.
- On the side of the map, click the gray arrow to expand the side panel. 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'll 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'll configure display settings on the View tab.
- Collapse the Contents pane.
- On the ribbon, click the View tab. 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.
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'll 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 Demographics.
- In the Demographics table, expand Standard. 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.
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 tutorial, you won't conduct a statistical analysis, but it is worth acknowledging the work of drawing lines in an equitable manner is complex, but important. You'll 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'll 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. Click Select geographies by rectangle.
The Select geographies by rectangle tool 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 tutorial.
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'll 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 about 50 percent for District 3 and TOTAL is between 714,000 and 728,000 residents for both districts. 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.
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 about 50 percent.
Your numbers do not need to match the example image exactly.
Your map may look similar to the following example image, but does not have to look identical.
- 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.
Congressional districts must be compact, contiguous, and equal. To help, Esri Redistricting includes tools that can test whether your plans meet those requirements.
- Click the Review tab. In the Analysis group, click Check Integrity.
Esri Redistricting produces a report of its integrity tests. In this case, your map does 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.
Depending on how you redrew the district boundary between District 2 and 3, your numbers may differ from the example image.
This table means that some districts have islands or pockets cut off from the rest of the district.
- In the Discontiguous Districts window, click the first district listed (in the example image, District 3). Click Next Part.
The main part of the first listed district is highlighted.
- Click Next Part again.
A smaller, discontiguous part of the district is highlighted. (You may see a different part than in the example image.)
You'll move the discontiguous part to its nearest district. In the example image, for instance, you would move the part from District 3 into the neighboring District 7.
- In the District Window, unlock the district that the discontiguous part is currently in (in the example image, District 3) and the district to which you want to move it (in the example image, District 7).
- Click the Create tab. In the Redistricting group, for District, choose the district to which you want to add the discontiguous polygon (in the example image, District 7).
- With the Select geography by picking them tool, click the discontiguous polygon or polygons.
The discontiguous polygon is added to its neighboring district, making it no longer discontiguous.
- In the Discontiguous Districts window, click Refresh.
One of the Number of Parts numbers goes down by one.
- Use the Discontiguous Districts window to identify the other discontiguous parts and add them to adjacent districts.
If you encounter two large discontiguous parts, such as the parts in District 8, you can also try adding parts to the district to make them contiguous, rather than moving all discontiguous parts to another district.
- 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.
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.
- On the ribbon, click the Review tab.
- 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.
Depending on how you drew your districts, your values may not match those shown in the example image.
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.
- On the ribbon, 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 tutorial, 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 a folder of your choice 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 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'll need to save it as your own map so you can edit the layers. Consider exploring the tutorial 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 tutorial, 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 tutorial 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 tutorials in the tutorial gallery.