91103 leans heavily Democratic by roughly 48 points: about 74% of voters vote Democratic and 26% Republican.
About 51% of adults in 91103 typically vote, below the U.S. average of about 62%. Among adults in 91103, ~38% vote Democratic, ~13% Republican, and ~49% don't vote. The map below shows estimated turnout by block group.
How 91103 compares
Among zip codes within 15 miles, 91103 leans more Democratic than 79 of 113 neighbors.
91103 runs about 29 points more Democratic than California as a whole.
Politics vary noticeably by block within 91103. The south side is the most Democratic-leaning (D+53) and the west side is the least Democratic-leaning (D+33), a spread of about 21 points.
Why 91103 leans the way it does
This analysis examined 14,881 data points per zip code to find what predicts political lean and turnout. The items below are a few correlations that stood out for 91103, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 98% of residents in 91103 live in densely developed areas, about 61 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and 91103 sits in the top quarter (about 38%, above 78% of zip codes). A high never-married share predicts Democratic voting, and about 48% of adults in 91103 have never been married, above 94% of zip codes.
Walkability and Democratic lean
Places with a highly walkable street grid tend to lean Democratic; 91103, CA sits in the top tenth nationally on this measure. A walkable street grid does not change how people vote; it mostly reflects how urban a place is.
Why turnout in 91103 looks the way it does
Areas with limited routine healthcare access turn out at lower rates. 91103 is in the bottom quarter nationally for routine-care measures such as insurance coverage, preventive screenings, and dental visits. Renters vote less often than owners, and about 52% of households in 91103 rent, about 27 points above the U.S. average of 25%. High food insecurity lines up with lower turnout, and about 26% of adults in 91103 report food insecurity, above 91% of zip codes. Learn more about the findings and methodology on the political spectrum map.
Nearby Zip Codes
Zip Codes with Similar Populations
Sources and methodology
Precinct-level voting records used to fit the model come from California Secretary of State, Elections, distributed by the Voting and Election Science Team. Demographic inputs come from the U.S. Census Bureau (ACS 5-year estimates and the 2020 Decennial Census). Health and environmental inputs come from the CDC (PLACES and the Environmental Justice Index). Land cover comes from the USGS and EPA. Election-day and lead-up weather come from PRISM 4km daily grids and the NOAA Global Historical Climatology Network. Mail-voting and election-administration patterns come from the MIT Election Lab's Survey of the Performance of American Elections. Block-group crime detail comes from CrimeGrade. Internet data and modeling support provided by ISPreports.org.
Modeling and analysis by the BestNeighborhood data science team. Full methodology and findings: political spectrum map.
Methodology reviewed by the BestNeighborhood data team. Last updated May 2026.