The data used by this project uses records of registered voters collected by the Los Angeles County Registrar of Voters which reflect records as of December of 2021. This voter file included a total of 5,676,108 registered voters, which included individual-level information such as party affiliation, preferred voting method, and date of original registration. Additionally, the voter information includes vote history over the last 20 years, including both presidential and non-presidential elections.
The project team used the Environmental Systems Research Institution (ESRI) geocoder to pinpoint individual voters to specific geographic locations in Los Angeles County. Voters who were unable to be geocoded were removed for the purposes of this mapping project. Of the 5,676,108 registered voters available, a total of 99.3% (or 5,635,387) were effectively geocoded.
The State of California does not require collection of racial-identifying information when individuals register to vote. Therefore, using surnames from the official Los Angeles County voter file, we estimated the probability of a voter’s race using Bayesian Improved Surname Geocoding (BISG). We employed a probability cutoff of 50% in order to assign a voter to a specific race.
We aggregated voters to the census tract level. Maps therefore present total voters within a given census tract in Los Angeles county. While there are 2,495 Census tracts in Los Angeles County, five of these Census tracts contain no population and were identified as “Non-Residential".
Each dot density map was created using random point fill, with the number of dots per census tract defined by a variable of interest. In the political party map, the random marker placement utilizes the absolute count method. One dot point represents ten voters. In the First-time Voter dot density maps we use density-based random marker placement. In these maps each dot represents one new voter.
For the registration rate map, we calculate percentage as the number of registered voters identified by race among the total population of the racial group in each tract. For the voter turnout map, we calculate the percentage as the total number of voters in 2020 divided by total number of registered voters by racial group. To calculate high Asian density tracts, the team subsetted Census tracts with greater than 40% total Asian population, 204 tracts in total were considered 40% or higher Asian density tracts.