Social Explorer offers a wide range of datasets and multiple ways to research and visualize them. It also lets you explore those datasets at different geographic levels, from states and counties to neighborhoods and, even block groups (where available).
Users can move between geographic levels while exploring maps or select places by name or Federal Information Processing Series (FIPS) code in reports. The level of detail available depends on the dataset release. American Community Survey (ACS) five-year estimates, for example, cover census tracts and block groups, along with ZIP Code Tabulation Areas (ZCTAs), school districts, tribal areas, and legislative districts. ACS one-year estimates cover larger areas and do not include tracts, block groups, or ZCTAs. The 2020 decennial census provides data down to the block group level.
Tracking Census Tracts Across Place and Time
If one geographic level deserves the spotlight, it is the census tract. Tracts give researchers a way to study communities at a scale smaller than a city or county and to compare those areas over time.
The Census Bureau defines a census tract as a “small, relatively permanent statistical subdivision of a county,” and that stability is key. The idea first took shape in New York City in the early 1900s. Dr. Walter Laidlaw wanted to compare neighborhood data across years, but changes to assembly district boundaries made that difficult. He proposed smaller areas whose boundaries would remain more consistent.
For the 1910 census, tract data were tabulated for New York City and seven other large cities: Baltimore, Boston, Chicago, Cleveland, Philadelphia, Pittsburgh, and St. Louis. The Census Bureau began including tract data in its standard decennial census publications in 1940. Tracts and similar block numbering areas together covered the nation by 1990; census tracts themselves were defined nationwide for Census 2000. Learn more about the history of census tracts.
Social Explorer subscribers can explore more than 80 years of historical tract data through maps and reports. Start with this 1940 map of New York City to examine the earliest Census Bureau release of tract-level data.
Tract Facts and Figures
Census tracts ideally contain about 4,000 people to help with more consistent comparisons, but that number sometimes varies from 1,200 to 8,000 due to geographic and other features. The 2024 ACS five-year estimates list 85,382 tracts in the U.S. Of those, 84,529 have a residential population greater than zero.
Tracts vary greatly in physical size across the country. In a dense city, one might span only a few blocks. In remote areas, a tract can cover thousands of square miles. Census Tract 2 in Alaska’s North Slope Borough, for example, covers more than 85,500 square miles of land—larger than the state of Nebraska! By comparison, Census Tract 615.05 in San Francisco County covers just 0.008 square miles (a few city blocks). In Manhattan, Census Tract 207.01 has 2,826 residents in 0.018 square miles—more than 154,000 people per square mile.
Explore the side-by-side maps of Alaska and San Francisco to see how tract sizes change with the landscape.
Although tracts are built to support comparisons over time, their boundaries must sometimes change along with population shifts. The Census Bureau reviews boundaries before each decennial census, with input from local participants in the Census Bureau’s Participant Statistical Areas Program. Growing areas may have tracts split, while areas with population loss may have tracts combined. These side-by-side maps of the booming areas in Harris County, Texas show tracts that were split between the 2010 and 2020 censuses.
Boundary changes matter when comparing data from different years. Social Explorer tools empower users to examine tract changes and adjust areas of focus. Additionally, Social Explorer’s U.S. Census Comparability Data lets users examine selected 2000 census measures on 2010 tract boundaries, including population, age, race and ethnicity, households, and housing. This makes it easier to compare those measures across the two censuses.
Explore More Tract-Level Data
Census and ACS data are only the beginning of neighborhood analysis. Social Explorer offers several other datasets at the tract level, including:
- EASI Estimates (2025) and Projections (2026–2030): demographic estimates and forecasts between ACS releases
- Home Mortgage Disclosure Act (2018–2025): mortgage applications and lending outcomes
- Picture of Subsidized Households (2015–2025): HUD-assisted housing and resident characteristics
- HUD Public Housing Buildings (2026): building locations that can be layered with tract data
- Social Vulnerability Index (2000–2022 from CDC; 2024 from Social Explorer): measures of community and health vulnerability to external stresses
- Community Resilience Estimates (2018–2024): estimates of individuals’ and households’ capacity to withstand and recover from disasters
- CDC PLACES (2020–2025): model-based estimates of health outcomes, risk behaviors, and, preventive care
Many of Social Explorer’s data resources also reach the block-group level for a closer look. Get started with Social Explorer’s maps and reports to find the right level of detail for your research. New to the platform? Sign up for a free Social Explorer account.