Analyze United States Census data

When redistricting, state legislatures or redistricting commissions are provided certain criteria with which to draw the lines. These criteria are intended to make the districts easy to identify and understand, and to ensure fairness and consistency.

All states must comply with the federal constitutional requirements related to population and antidiscrimination. For congressional redistricting, the Apportionment Clause of Article I, Section 2, of the United States Constitution requires that all districts be as nearly equal in population as practicable, which essentially means exactly equal. For state legislative districts, the Equal Protection Clause of the Fourteenth Amendment to the Constitution requires that districts be substantially equal. Some say that 10 percent deviation in population from one district to the next is a safe standard. However, that has not proven to be a guaranteed protection from court scrutiny or revision. Many states provide their own deviation standard. For instance, Colorado prohibits districts from having a population deviation above 5 percent (Colo. Const. Art. V, § 46).

In addition to population equality, Section 2 of the Voting Rights Act of 1965 prohibits plans that intentionally or inadvertently discriminate on the basis of race, which could dilute the minority vote.

In addition to these mandatory standards set out by the Constitution and the Voting Rights Act, 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 be adopted by the legislature, chamber, or committee. For instance, Maryland requires that "each legislative district shall consist of adjoining territory, be compact in form, and of substantially equal population. Due regard shall be given to natural boundaries and the boundaries of political subdivisions." (Md. Const. art. III, §§ 3–5)

To help you draw new districts, you'll use Esri Redistricting, a web-based solution that enables governments, advocates, and citizens to complete and share regulation-compliant redistricting plans. The Esri Redistricting app includes detailed help documentation. You'll open the app, add census data, and draw districts based on population.

Open a plan

Maryland, one of American's 13 original colonies, is diverse state stretching from the Atlantic Ocean to the Appalachian Mountains. The Old Line State has approximately 6 million residents, so 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 the ease of training, you'll map seven districts in this lesson.)

You'll open Esri Redistricting, also known as Redistricting Online, and start a new redistricting plan.

  1. 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 account. Your 60-day membership gives you access to Esri Redistricting Online. You may have to wait one business day before being granted access.

  2. At the top of the page, click the Apps button.

    Apps button

  3. Click Redistricting Online.

    Redistricting Online

  4. In the Open Plan window, click Create Plan.

    Create Plan button

    The New Plan window opens. From here, you'll create seven districts within the state of Maryland.

  5. In the New Plan window, set the following parameters:
    • Verify that District caption is set to District.
    • For Number of districts, choose 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-Group-Block.
  6. Click Next.

    New Plan window

    The next window has options to modify the colors of the districts.

  7. In the New Plan window, 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 ease of training, you'll limit your work to white and black demographic groups.

  8. Under Select demographics to display, under the Sum column, scroll down and check the boxes for WHITE and BLACK.

    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.

    WHITE and BLACK boxes checked

  9. Click Done.

    The Save Plan dialog box opens. You can opt to save the plan during plan creation or at a later point. For this exercise, you'll save the plan later.

  10. 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 different districts.

    In the District Window, the target mean of 824,793 residents per district is listed. 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.

    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.

  11. Click the View tab.
  12. Check the Show Target Values box.

    Show Target Values box checked

    The mean value of 824,793 is now a permanent fixture in the Target column of the District Window.

    Now that you have identified your population targets, you'll spread the populations among seven districts you will create in the next step.

Create districts

The Esri Redistricting workflow is part of the ribbon. You'll follow the workflow to create districts.

  1. On the ribbon, click the Learn tab and review its contents.

    Learn tab

    The Learn tab contents discuss the Esri Redistricting workflow and offer a quick tour and answers to frequently asked questions.

  2. 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.

  3. In the Redistricting group, click the Select geography button.

    Select geography button

  4. In the Redistricting group, next to District, choose District 1.

    District 1


    Alternatively, in the District Window, you can click any row to activate that district.

  5. In the District Display group, click Show Totals.

    Show Totals check

    By checking the box for Show Totals, you will see the accumulated population for the district you're creating.

  6. 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.

    Map showing District 1


    If you want to make a change, in the Redistricting group, click the Undo and Redo buttons.

    Undo and Redo buttons
  7. Select District 2 and click the county immediately northwest of Washington, D.C. (It has a population of 971,777.)

    Map showing District 2

  8. Select District 3 and click the City of Baltimore.

    Map showing District 3


    Counties are added to a district when you click them. If you want 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 then click the map to populate that district. Remember: You're looking for district numbers between 600,000 and 1,000,000 residents.

  9. Populate districts 4 through 7.

    You may need several minutes to find the correct population balance among Maryland's 24 counties.


    If necessary, use the navigation buttons on the upper left corner of the map, or in the Tools group, to pan and zoom. If you use those navigation buttons, you'll have to again click the Select geography button to resume your work.

    Map navigation tools

    When complete, your map shows the desired balance among the seven districts.

    Map showing seven congressional 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.

  1. In the upper left corner, click the Save As button.

    Save As button


    Alternatively, in the File menu, in the Plans group, you can click the Save As button.

  2. In the Save Plan window, set the following parameters:
    • For Name, type First draft.
    • For Folder, verify that My Plans is chosen.
    • For Description, type First draft of redistricting plan for seven congressional districts in Maryland.
    • Click OK.

    Save Plan window

  3. If you're not going continuing to the next lesson, click Sign Out in the upper right corner; otherwise, leave your map open.

You've created a redistricting plan for Maryland. You balanced the districts so you could ensure equal representation among the seven congressional districts.


This is an exercise designed to help you understand the redistricting process. Balancing districts to meet all the criteria required by the Voting Rights Act and your state's constitution is difficult and time consuming. Don't spend your initial learning time balancing districts. You will make that comparison as part of a later lesson.

Next, you'll download Maryland's 2012 Congressional District Plan. From that plan, you'll unlock District 3, Baltimore and the greater Baltimore area, and create a new majority-minority District 3 by exchanging populations with an adjoining district. In doing so, the new District 3 would meet the Voting Rights Act requirements because it would have a black population numbering between 40 percent and 50 percent. A black population number below 40 percent is considered too low to ensure the likelihood of a black representative winning the district during a congressional election. A 50 percent number is considered too high because that would pack one district with so many black residents that it would dilute black representation from the surrounding districts.

Balance a district

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 configure a new District 3 to ensure that it contains a black population between 40 percent and 50 percent.

Organize a map

You'll download a PLAN file, a format your computer may not recognize. However, the file will be recognized by Esri Redistricting.

  1. Download the 111th Maryland Congressional District plan and save it to a convenient location, such as your desktop.
  2. If necessary, sign in to Esri Redistricting and, on the File tab, and in the Plans group, click Open.
  3. In the Open Plan window, click Open Local Plan and browse to where you saved the PLAN file locally on your computer.
  4. Extract the PLAN folder from the zipped document and upload the file.

    After the PLAN file loads, a map of Maryland's 2012 congressional districts appears.

    Congressional map of Maryland

    Your map shows the lines of eight congressional districts imposed over Maryland. The diagonal lines mean those districts are locked and cannot be edited.

  5. On the left edge of the map, click the gray arrow to open the Map Contents pane.

    Map navigation tools

    The Map Contents pane contains three layers as well as the Streets basemap. You'll be working with the Districts layer, which contains data derived from the 111th Maryland Congressional District PLAN file you just downloaded.

    Map Contents pane

  6. Click the Create tab, and in the District Display group, verify Display Locks and Display Names are checked. Click Show Totals.

    District Display group

    You have a working map.

    Map with district names and populations


    Every district should have diagonal lines indicating that the data in each district is locked. If necessary, in the table, verify that each box in the Lock column is checked.

    Next, you'll save and label the map.

  7. On the File tab, in the Plans group, click Save As.

    Save As button

  8. In the Save Plan window, set the following parameters:

    • For Name, type Proposed Congressional Districts (your initials).
    • For Folder, confirm My Plans is selected.
    • For Description, type First draft of a new District 3 creating a new majority-minority congressional district in Maryland.
    • Click OK.

    Save Plan

    The plan is saved under the new name, which is listed in the upper right corner.

    New map name

    Next, you'll unlock District 3 and zoom to its location.

  9. Click the Create tab. In the Redistricting group, for District, choose District 3.
  10. Click Zoom to the selected district.

    Zoom to the selected district button

    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.

    Map of District 3

  11. If necessary, pan and zoom your map so District 3 is in the center. (You can click the Pan button in the Tools group or in the navigational tools on the left.)
  12. Close the Map Contents pane by clicking 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.

    Your goal is to convert District 3 into a majority-minority district with a black population between 40 percent and 50 percent. To show these percentages, you will open the Demographics table and add percentages to the District Window reflecting the percentage of black and white populations.

  13. In the Statistics group, click the Demographics button.

    Demographics button

  14. In the Demographics table, expand the Alternative folder. In the Percent column, check WHITE and BLACK and click Ok.

    BLACK and WHITE percentage boxes checked

    The District Window adds columns showing percentages of black and white populations. Note that District 3 is 55.97 percent black—nearly six points above the mandated maximum percentage of 50 percent. To correct this imbalance, you'll relocate areas with high percentages of whites in District 2 and add them to District 3. And to keep the populations of those districts in balance, you'll relocate black populations in District 3 and add them to District 2.

Adjust district populations

Creating majority-minority districts is a complex process; for the sake of simplicity, this lesson will focus solely on black and white populations. Also for simplicity, you'll work only with districts 2 and 3 instead of readjusting populations residing in other districts.

Creating a majority-minority district means identifying and locating high concentrations of the demographic groups you need to move among the districts.

In the case of Maryland, the greater Baltimore area, circled in yellow, is a region where blacks have traditionally lived. The red circle encompasses portions of Howard, Frederick, and Carroll counties, areas with high concentrations of whites. You'll move those two populations between these districts.

Areas of Maryland showing white and black populations

Adjusting congressional districts to meet federal requirements can be time-consuming. For this lesson, expand District 2 along the southern edge of District 3 so the new District 2 would include sizeable portions of southern Baltimore. This suggestion, along with transferring corresponding white areas from District 2 into District 3, could save you considerable time and should get you close to the balance required for a majority-minority district.

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 sizable chunks or small pieces from one district to the other. While doing so, you'll keep an eye on the TOTAL and BLACK_P columns.

  1. In the District Window, in the Lock column, verify that all the boxes for each district are checked.

    District Statistics table with all districts locked

  2. Uncheck the Lock box for districts 2 and 3.

    The diagonal lines reflecting locked data disappear for those two districts; however, only one district can be active at a time.

  3. On the Create tab, in the Redistricting group, verify that District 3 is active and click Select geographies by rectangle.

    Select geographies by rectangle button

    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.

  4. Zoom to the area where districts 2 and 3 share a boundary.

    Boundary between districts 2 and 3


    To maximize map space, you can minimize the District Window by dragging down its handle; ensure that districts 2 and 3 remain visible.

  5. Using the Select geographies by rectangle tool, and with District 3 active, draw a rectangle around the Eldersburg area.


    Your map, reflecting the area you drew, could vary considerably from this map. Keep in mind that there are many right answers in redistricting, so your map may look different than the ones presented in this lesson. What's important is your goal is to convert District 3 into a majority-minority district (black population between 40 percent and 50 percent) while maintaining populations of about 720,000 people (the margin may vary, plus or minus, about 8,000 people) in each district.

    In the District Window, the populations in the TOTAL and BLACK_P columns change when a district boundary is redrawn.

    Table showing properly aligned districts

    Next, you'll activate District 2. This time, you'll use the Select geographies by polygon tool to make incremental changes.

  6. In the Redistricting group, click the District box and choose District 2.
  7. 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.

    Select geographies by polygon tool

  8. Using the two selection tools, move areas between District 2 and District 3 until BLACK_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 among 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 into the Block or Block Group level when you make your selections. You may also change the selection level in the Selection Level slider.

    Selection Level slider

    When complete, your map could resemble this map, which focuses on the changed boundary between District 2 (in light green) and District 3 (in purple). Your map colors could vary. This map focuses on downtown Baltimore, which in this example, was transferred from District 3 to District 2 so District 3 would qualify as majority-minority.

    Map showing possible changes between District 2 and District 3

    When both districts are compliant, your District Window shows that the total populations of District 2 and District 3 fall between 714,000 and 728,000 and the total black population of District 3 is between 40 percent and 50 percent.

    Table reflecting a correct district realignment

  9. Check the boxes to lock District 2 and District 3.
  10. Save the plan.

You've created a majority-minority district in Maryland, which could increase that state's black congressional representatives to the United States Congress.

Test congressional plans

Previously, you moved populations between District 2 and District 3 so you could create a majority-minority district 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 their 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.

  1. If necessary, open your plan.
  2. Click the Review tab and click Check Integrity.

    Check Integrity button

    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.

    Integrity test results

  3. For Connectivity Check, click Details.

    Discontiguous Districts table

    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.

  4. In the District Window, unlock districts 2 and 3 and fix those isolated areas.
  5. Zoom in to those districts and pan the boundaries until you locate those isolated areas.

    Isolated areas

  6. 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.
  7. Rerun the Check Integrity test.

    Refresh results

    If you find more islands, you can also use the Next Part button in the Discontiguous Districts table to find them.

  8. In the Discontiguous Districts table, click any district and then 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.

  9. Using the Discontiguous Districts table, click the Next Part button to find and fix each isolated area.
  10. When your table is empty, rerun the integrity test.

    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.

    Successful integrity test result

    A results box with six green check marks means you have successfully completed this battery of tests.

  11. Lock all the districts in the District Window.
  12. Close all the tables and save your plan.

Run the Compactness test

Compactness is one of the primary 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. Redistricting Online 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 Redistricting Online, you have one button that will run a test listing a variety of compactness scores.

  1. If necessary, click the Review tab.
  2. 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.

    Compactness scores

    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.

  3. Close the table.
  4. 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 efforts should increase the likelihood that your plan passes the review of your staffing peers, the state legislature, and the governor. In addition, creating a credible plan now could also help your plan survive a court challenge later.

Publish to the portal

Previously, you successfully tested your congressional plan. Next, you'll publish your map so fellow analysts can review your work. You'll share a portal, 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.

  1. If necessary, open your plan.
  2. 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 via 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.

  3. In the Community group, click Publish Feature Layer.

    Publish Feature Layer button

  4. In the ArcGIS Online - Feature Service window, click Next.

    Title and description fields

    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 to the public, you'll use this same workflow, but you'll check the Everyone (public) box.

  5. Save to your folder and click Next.

    Saving feature service details to your folder

  6. 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.

    Use Constraints and Summary fields

    After a few moments, a window appears indicating the feature service was successfully published.

  7. In the window, click the link.

    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.

  8. Click Open in Map Viewer.

    Open in Map Viewer button

    Your feature layer opens in ArcGIS Online.

    Map of Maryland's eight congressional districts

  9. Zoom in and click anywhere within District 3.

    Pop-up showing District 3

    The pop-up opens and shows the percentage of the black population qualifies the district as a majority-minority district.


    At this point, your ArcGIS Online map is passive. If you want 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. Get Started with ArcGIS Online shows users how to configure map appearance and pop-ups as well as creating and sharing maps.

    In the portal, your fellow staffers can create their own maps. 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.

In this lesson, you created a new redistricting map based on 2010 United States Census data. You also created and tested a majority-minority district that was shown to be compliant with the Voting Rights Act of 1965. 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 via 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.

You can find more lessons in the Learn ArcGIS Lesson Gallery.