Assigning Voters to the Correct Districts
After all geographic boundaries are aligned as best as possible, the next job is to place voters in the correct precinct. In most cases, it is that precinct that then defines the many electoral districts the voter is in—congressional, legislative, etc. Districts nest within each other, but not always neatly, as is the case when a school district overlaps two municipalities. In some cases, even a single precinct can be "split" and contain multiple electoral districts, particularly for more local offices. Since the creation, maintenance, and naming of precincts and electoral districts happens across varying levels of government, it can be helpful to use a standardized naming schema such as Open Civic Data Division Identifiers in addition to more colloquial names. That way, different systems can know they're both talking about the same "School District 1" or "Western Precinct," should they need to communicate across governmental departments or levels.
Each voter’s address can be thought of as a geographic point, one that could be defined by latitude and longitude; this is similar to how your location can be “pinned” on a Google map or other map app. If GIS is available for use by local election officials, then each voter’s address is assigned a point, which is immediately and automatically assigned to the right precinct. This is called “geocoding,” and states can adopt different strategies to do it. See NSGIC’s Best Practices for Geo-Enabling Elections for more.
Note, too, that Next Generation 911 (aka NextGen 911 or NG911) is being adopted by states and localities to better provide emergency services. Getting NextGen 911 up and running means each residence will be geo-coded. It could be possible for this information to be shared with election officials.
It is all but certain that the state’s redistricting entity has its new maps and data available in a digital format, even if the bill adopting the new maps uses some other system, such as metes and bounds, to identify the plan.
It is less likely that election officials have the capacity to receive the maps geographically and work with them in GIS. In 2021, the Geo-Enabled Elections project—a part of the National States Geographic Information Council (NSGIC)—surveyed state election directors on how their states used geographic information systems to manage elections processes and received 27 responses. Of those, three-fourths indicated their voter registration systems did not support GIS data.
In the many jurisdictions where GIS is not available, voter assignment to precincts is done by hand, based on tabular—not spatial—information about voter addresses. This process leaves room for error.
Some local election offices may simply have maps on a wall, with district and precinct boundaries superimposed on it, possibly with marker on an acetate overlay, although in Shasta County, Calif., the old paper maps are hand-colored with colored pencils at least through the 2010 post-redistricting cycle. A clerk looks at a voter’s address, finds the corresponding precinct, and assigns the voter to that precinct in the voter registration database. This generally works, but, according to Election Data Services, some residences are on borders of precincts, leading to 12% of voters being misassigned. Also, if a voter gets a ballot that doesn’t include the races they expect, that is a problem—and it hurts voter confidence.
Many offices have moved to keeping street segment files in a database to determine what districts a given voter is in. A “street segment” is a range of addresses on a single street where all voters within the range are assigned to the same precinct or district. All addresses within a jurisdiction should be able to be placed within a defined street segment, and an address should never be in more than one segment. Since precinct or district lines often run through the middle of streets, some voters with similar addresses may be assigned differently depending on the side of the street they live on. Typically, this is represented by adding an “odd”, “even”, or “both” parameter to a street segment.
For jurisdictions with addresses that do not follow normalized naming or numbering conventions, individual address points may be represented as street “segments”, though having a high number of such single-residence points can make lists harder to maintain and more likely to introduce accidental inaccuracies.
A street segment file containing the following segments to assign addresses to precincts:
Start House Number
|
End House Number
|
Street Name
|
Street Suffix
|
Odd, Even, Both
|
Precinct ID
|
1500 |
2000 |
7th |
Avenue |
Both |
C |
1651 |
1959 |
12th |
Avenue |
Odd |
C |
453 |
453 |
Elm |
Street |
Both |
C |
1901 |
1999 |
Main |
Street |
Odd |
C |
1900 |
1998 |
Main |
Street |
Even |
G |
Which in turn can be used to place voters into their correctly updated districts as below:
ID
|
Last Name
|
First Name
|
Street
|
Number
|
Precinct
|
Old District
|
New District
|
3931154 |
Smith |
John |
7th Avenue |
1858 |
C |
1 |
3 |
4420947 |
Adams |
Samuel |
12th Avenue |
1659 |
C |
1 |
3 |
3342913 |
Adams |
Martha |
Elm Street |
453 |
C |
1 |
3 |
4301660 |
Rodriguez |
Edward |
Main Street |
1901 |
C |
1 |
3 |
4404091 |
McDonald |
Michael |
Main Street |
1902 |
G |
1 |
1 |
Maintaining geographic information in a list format is not wrong, but it can introduce errors because address changes and additions cannot be viewed spatially. For instance, if there is an error in translating geography into a list, it will likely not be identified. And updating street segment files after redistricting (or reprecincting) is laborious—but also necessary for added assurance and transparency. An election management system may manage much of this work, but without an audit (see below) it is hard to find misassignments. New or extended segments may be needed to be regularly created to reflect new construction or changes to land use, even outside of a redistricting cycle, so offices should be prepared to regularly implement these procedures for maintaining and assuring accuracy of assignments between elections.
Still other states may produce their redistricting maps as “block equivalency files,” in which each census block is assigned to congressional, state Senate and state House districts. This is more precise for redistricting purposes since census blocks account for all geography in the nation. When election officials receive data in these files, they can use the same census blocks to create precincts—but it doesn’t solve the need to assign voters’ addresses to the right precinct.