How BlockAtlas computes its numbers

A number is native when BlockAtlas shows it for the geography on which its source published it. A number is computed by BlockAtlas when we combine published values for another area, boundary, or time comparison. This describes where the arithmetic happened. It is separate from whether the source is a survey estimate: American Community Survey values are estimates in both cases.

Population in a custom area

Population uses 2020 Census blocks whose centers fall inside the area. For very large areas, it uses whole 2022 tracts whose centers fall inside the area.

Each block or tract counts in full. A boundary can include part of a unit without its center. The result is an estimate, especially where Census units cover large areas.

Demographics in a custom area

BlockAtlas reads 2020–2024 American Community Survey counts from 2024 block groups for most indicator families. Other families use 2022 tracts because the needed cells are not available for block groups.

For a standard area, BlockAtlas counts each source unit inside the area in full. It weights each boundary unit by its share of 2020 block population inside the area. When population cannot supply that weight, it uses block land area and then spatial overlap.

For a very large area, BlockAtlas selects whole 2022 tracts whose centers fall inside the area. Maps that start from block groups use their prebuilt 2022 tract values. This faster method is an estimate.

BlockAtlas sums counts. It recomputes rates from their allocated numerator and denominator. It rebuilds a median from allocated count ranges. It leaves a value unavailable when the published data cannot support one of these methods.

Demographic change over time

Change maps compare non-overlapping American Community Survey windows. The change itself is computed by BlockAtlas. A count change is a percent change. A percentage change is a percentage-point change. Another count-backed rate uses the difference between its two values.

Each map uses current boundaries. Most current endpoints start from 2024 block groups. The others use 2022 tracts. A historical endpoint starts from that window's block groups when they publish every required cell. Otherwise, it starts from that window's tracts. A changed boundary splits a source unit by land overlap. Rates move their numerator and denominator separately. Historical medians move their count ranges before BlockAtlas rebuilds them, but BlockAtlas does not publish a direct change map for those medians. BlockAtlas shows change only when the source cells, definitions, and units are compatible.

Missing data and coverage

A negative Census source cell is a missing-value code, so BlockAtlas changes it to missing before arithmetic. A negative result calculated from valid source values remains valid. A missing or zero denominator makes a rate unavailable. A missing distribution component makes the row unavailable.

A reallocated map cell needs at least 99% source coverage. A custom-area result with less than 90% coverage is unavailable. A printable result with at least 90% but less than 99.5% coverage carries an approximately equal sign (≈). BlockAtlas does not scale partial data up to 100%.

Other data we use

Reachable areas (drive, walk, and bike times) use OpenStreetMap road data with the Valhalla routing engine. © OpenStreetMap contributors.
Place names, for labeling a dropped pin or point, are reverse geocoded with Pelias against Who's On First.
Points of interest come from the latest OpenStreetMap snapshot that BlockAtlas imported. The snapshot can lag behind live OpenStreetMap data. © OpenStreetMap contributors.
Day and night population shift subtracts Census LEHD LODES residence jobs from workplace jobs. It divides the result by 2020–2024 ACS population. Alaska uses 2016 LODES data, Michigan uses 2021, and every other state and DC uses 2023.
Base maps (light, dark, and satellite) and forward geocoding (finding a location from an address) are provided by Stadia Maps.

Try it yourself: population by drive time or population by radius. Questions welcome at [email protected].

Appendix: how each tract map is built

This appendix includes every generated United States tract map once. It groups each map by the stored route that builds its tract view. Some current maps also show direct block-group values when you zoom in. Open a map's information panel for its variables and complete source details.

The label beside each map identifies its final calculation. A rebuilt median comes from published count ranges. A plurality selects the largest category. Dot density places a fixed number of dots from published category counts.

Current ACS from block groups (70 maps)

Reads 2020–2024 ACS counts from 2024 block groups and reallocates them to 2022 tract boundaries before it calculates the map value.

% Age 65+ Rate
% Built Since 2010 Rate
% Carpooling to Work Rate
% Commute 1hr+ Rate
% Driving Alone to Work Rate
% Family Households Rate
% Homes for Seasonal or Occasional Use Rate
% Homes in Buildings of 5+ Units Rate
% Households Earning $100k+ Rate
% Households Earning $200k+ Rate
% Households Earning Under $35k Rate
% Households Moving In During the ACS Window Rate
% Households With 2+ Vehicles Rate
% Households with Children Rate
% Households: Married Couple with Children Rate
% Households: No Internet Access Rate
% Households: Single Parent with Children Rate
% Housing Units Vacant Rate
% In Labor Force (Age 16+) Rate
% In Management, Business, Science or Arts Occupations Rate
% In Service Occupations Rate
% Leaving for Work Before 7am Rate
% Married, Spouse Present (Age 15+) Rate
% Never Married (Age 15+) Rate
% Nonfamily Households Rate
% One-Person Households Rate
% Owner Occupied Rate
% Owner-Occupied Homes With a Mortgage Rate
% Owners Spending 30%+ of Income on Housing Rate
% Owners Spending 50%+ of Income on Housing Rate
% Rent-Burdened (30%+ of Income) Rate
% Renter Occupied Rate
% Renters Spending 50%+ of Income on Rent Rate
% Self-Employed Rate
% Single-Family Homes Rate
% Taking Public Transit to Work Rate
% Under 18 Rate
% Unemployed (of Civilian Labor Force) Rate
% Veterans (Age 18+) Rate
% Walking or Biking to Work Rate
% With Bachelor's or Higher Rate
% With Graduate or Professional Degree Rate
% With No High School Diploma or GED Rate
% Without Health Insurance Rate
% Working From Home Rate
% Working in Construction Rate
% Working in Food Service, Arts or Accommodation Rate
% Working in Health Care or Education Rate
% Working in Manufacturing Rate
% Working in Professional or Business Services Rate
% Working in Retail Trade Rate
Age (plurality) Plurality
Age (total) Count
Average Household Size Rate
Commute Mode (dots) Dot density
Commute Mode (plurality) Plurality
Households Count
Housing Tenure (dots) Dot density
Housing Tenure (plurality) Plurality
Housing Units Count
Median Age Rebuilt median
Median Gross Rent Rebuilt median
Median Home Value Rebuilt median
Median Household Income Rebuilt median
Median Year Built Rebuilt median
Per Capita Income Rate
Population Count
Race and ethnicity (dots) Dot density
Race and ethnicity (plurality) Plurality
Race and ethnicity (total) Count

Current ACS from tracts (15 maps)

Reads 2020–2024 ACS values directly for 2022 tracts. No boundary reallocation is needed.

% Below Poverty Level Rate
% Enrolled in College or Graduate School Rate
% Enrolled in K-12 Rate
% Foreign-Born Rate
% Households With 2+ Workers Rate
% Households: No Vehicle Available Rate
% Living in Group Quarters Rate
% Speaking a Non-English Language at Home Rate
% Speaking English Less Than "Very Well" Rate
% Who Moved in the Past Year Rate
% With a Disability Rate
Language spoken at home (dots) Dot density
Language spoken at home (plurality) Plurality
Language spoken at home (total) Count
Mean Commute (Minutes) Rate

Historical ACS from block groups (118 maps)

Reads 2010–2014 or 2015–2019 ACS counts from that window's block groups and reallocates them to 2022 tract boundaries.

% Age 65+ (2010–2014) Rate
% Age 65+ (2015–2019) Rate
% Built Since 2010 (2010–2014) Rate
% Built Since 2010 (2015–2019) Rate
% Carpooling to Work (2010–2014) Rate
% Carpooling to Work (2015–2019) Rate
% Commute 1hr+ (2010–2014) Rate
% Commute 1hr+ (2015–2019) Rate
% Driving Alone to Work (2010–2014) Rate
% Driving Alone to Work (2015–2019) Rate
% Family Households (2010–2014) Rate
% Family Households (2015–2019) Rate
% Homes for Seasonal or Occasional Use (2010–2014) Rate
% Homes for Seasonal or Occasional Use (2015–2019) Rate
% Homes in Buildings of 5+ Units (2010–2014) Rate
% Homes in Buildings of 5+ Units (2015–2019) Rate
% Households Earning $100k+ (2010–2014) Rate
% Households Earning $100k+ (2015–2019) Rate
% Households Earning $200k+ (2010–2014) Rate
% Households Earning $200k+ (2015–2019) Rate
% Households Earning Under $35k (2010–2014) Rate
% Households Earning Under $35k (2015–2019) Rate
% Households Moving In During the ACS Window (2010–2014) Rate
% Households Moving In During the ACS Window (2015–2019) Rate
% Households With 2+ Vehicles (2010–2014) Rate
% Households With 2+ Vehicles (2015–2019) Rate
% Households with Children (2010–2014) Rate
% Households with Children (2015–2019) Rate
% Households: Married Couple with Children (2010–2014) Rate
% Households: Married Couple with Children (2015–2019) Rate
% Households: No Internet Access (2015–2019) Rate
% Households: Single Parent with Children (2010–2014) Rate
% Households: Single Parent with Children (2015–2019) Rate
% Housing Units Vacant (2010–2014) Rate
% Housing Units Vacant (2015–2019) Rate
% In Labor Force (Age 16+) (2010–2014) Rate
% In Labor Force (Age 16+) (2015–2019) Rate
% In Management, Business, Science or Arts Occupations (2010–2014) Rate
% In Management, Business, Science or Arts Occupations (2015–2019) Rate
% In Service Occupations (2010–2014) Rate
% In Service Occupations (2015–2019) Rate
% Leaving for Work Before 7am (2010–2014) Rate
% Leaving for Work Before 7am (2015–2019) Rate
% Married, Spouse Present (Age 15+) (2010–2014) Rate
% Married, Spouse Present (Age 15+) (2015–2019) Rate
% Never Married (Age 15+) (2010–2014) Rate
% Never Married (Age 15+) (2015–2019) Rate
% Nonfamily Households (2010–2014) Rate
% Nonfamily Households (2015–2019) Rate
% One-Person Households (2010–2014) Rate
% One-Person Households (2015–2019) Rate
% Owner Occupied (2010–2014) Rate
% Owner Occupied (2015–2019) Rate
% Owner-Occupied Homes With a Mortgage (2010–2014) Rate
% Owner-Occupied Homes With a Mortgage (2015–2019) Rate
% Owners Spending 30%+ of Income on Housing (2010–2014) Rate
% Owners Spending 30%+ of Income on Housing (2015–2019) Rate
% Owners Spending 50%+ of Income on Housing (2010–2014) Rate
% Owners Spending 50%+ of Income on Housing (2015–2019) Rate
% Rent-Burdened (30%+ of Income) (2010–2014) Rate
% Rent-Burdened (30%+ of Income) (2015–2019) Rate
% Renter Occupied (2010–2014) Rate
% Renter Occupied (2015–2019) Rate
% Renters Spending 50%+ of Income on Rent (2010–2014) Rate
% Renters Spending 50%+ of Income on Rent (2015–2019) Rate
% Self-Employed (2010–2014) Rate
% Self-Employed (2015–2019) Rate
% Single-Family Homes (2010–2014) Rate
% Single-Family Homes (2015–2019) Rate
% Taking Public Transit to Work (2010–2014) Rate
% Taking Public Transit to Work (2015–2019) Rate
% Under 18 (2010–2014) Rate
% Under 18 (2015–2019) Rate
% Unemployed (of Civilian Labor Force) (2010–2014) Rate
% Unemployed (of Civilian Labor Force) (2015–2019) Rate
% Veterans (Age 18+) (2010–2014) Rate
% Veterans (Age 18+) (2015–2019) Rate
% Walking or Biking to Work (2010–2014) Rate
% Walking or Biking to Work (2015–2019) Rate
% With Bachelor's or Higher (2010–2014) Rate
% With Bachelor's or Higher (2015–2019) Rate
% With Graduate or Professional Degree (2010–2014) Rate
% With Graduate or Professional Degree (2015–2019) Rate
% With No High School Diploma or GED (2010–2014) Rate
% With No High School Diploma or GED (2015–2019) Rate
% Without Health Insurance (2010–2014) Rate
% Without Health Insurance (2015–2019) Rate
% Working From Home (2010–2014) Rate
% Working From Home (2015–2019) Rate
% Working in Construction (2010–2014) Rate
% Working in Construction (2015–2019) Rate
% Working in Food Service, Arts or Accommodation (2010–2014) Rate
% Working in Food Service, Arts or Accommodation (2015–2019) Rate
% Working in Health Care or Education (2010–2014) Rate
% Working in Health Care or Education (2015–2019) Rate
% Working in Manufacturing (2010–2014) Rate
% Working in Manufacturing (2015–2019) Rate
% Working in Professional or Business Services (2010–2014) Rate
% Working in Professional or Business Services (2015–2019) Rate
% Working in Retail Trade (2010–2014) Rate
% Working in Retail Trade (2015–2019) Rate
Average Household Size (2010–2014) Rate
Average Household Size (2015–2019) Rate
Households (2010–2014) Count
Households (2015–2019) Count
Housing Units (2010–2014) Count
Housing Units (2015–2019) Count
Median Age (2010–2014) Rebuilt median
Median Age (2015–2019) Rebuilt median
Median Gross Rent (2015–2019) Rebuilt median
Median Home Value (2015–2019) Rebuilt median
Median Household Income (2010–2014) Rebuilt median
Median Household Income (2015–2019) Rebuilt median
Median Year Built (2015–2019) Rebuilt median
Per Capita Income (2010–2014) Rate
Per Capita Income (2015–2019) Rate
Population (2010–2014) Count
Population (2015–2019) Count

Historical ACS from tracts (22 maps)

Reads 2010–2014 or 2015–2019 ACS counts from that window's tracts and reallocates them to 2022 tract boundaries.

ACS change from block groups (103 maps)

Reallocates the current and historical block-group counts to 2022 tract boundaries, then compares the two endpoints.

% Age 65+ (10-year change) Point change
% Age 65+ (5-year change) Point change
% Built Since 2010 (10-year change) Point change
% Built Since 2010 (5-year change) Point change
% Carpooling to Work (10-year change) Point change
% Carpooling to Work (5-year change) Point change
% Commute 1hr+ (10-year change) Point change
% Commute 1hr+ (5-year change) Point change
% Driving Alone to Work (10-year change) Point change
% Driving Alone to Work (5-year change) Point change
% Family Households (10-year change) Point change
% Family Households (5-year change) Point change
% Homes for Seasonal or Occasional Use (10-year change) Point change
% Homes for Seasonal or Occasional Use (5-year change) Point change
% Homes in Buildings of 5+ Units (10-year change) Point change
% Homes in Buildings of 5+ Units (5-year change) Point change
% Households Moving In During the ACS Window (10-year change) Point change
% Households Moving In During the ACS Window (5-year change) Point change
% Households With 2+ Vehicles (10-year change) Point change
% Households With 2+ Vehicles (5-year change) Point change
% Households with Children (10-year change) Point change
% Households with Children (5-year change) Point change
% Households: Married Couple with Children (10-year change) Point change
% Households: Married Couple with Children (5-year change) Point change
% Households: No Internet Access (5-year change) Point change
% Households: Single Parent with Children (10-year change) Point change
% Households: Single Parent with Children (5-year change) Point change
% Housing Units Vacant (10-year change) Point change
% Housing Units Vacant (5-year change) Point change
% In Labor Force (Age 16+) (10-year change) Point change
% In Labor Force (Age 16+) (5-year change) Point change
% In Management, Business, Science or Arts Occupations (10-year change) Point change
% In Management, Business, Science or Arts Occupations (5-year change) Point change
% In Service Occupations (10-year change) Point change
% In Service Occupations (5-year change) Point change
% Leaving for Work Before 7am (10-year change) Point change
% Leaving for Work Before 7am (5-year change) Point change
% Married, Spouse Present (Age 15+) (10-year change) Point change
% Married, Spouse Present (Age 15+) (5-year change) Point change
% Never Married (Age 15+) (10-year change) Point change
% Never Married (Age 15+) (5-year change) Point change
% Nonfamily Households (10-year change) Point change
% Nonfamily Households (5-year change) Point change
% One-Person Households (10-year change) Point change
% One-Person Households (5-year change) Point change
% Owner Occupied (10-year change) Point change
% Owner Occupied (5-year change) Point change
% Owner-Occupied Homes With a Mortgage (10-year change) Point change
% Owner-Occupied Homes With a Mortgage (5-year change) Point change
% Owners Spending 30%+ of Income on Housing (10-year change) Point change
% Owners Spending 30%+ of Income on Housing (5-year change) Point change
% Owners Spending 50%+ of Income on Housing (10-year change) Point change
% Owners Spending 50%+ of Income on Housing (5-year change) Point change
% Rent-Burdened (30%+ of Income) (10-year change) Point change
% Rent-Burdened (30%+ of Income) (5-year change) Point change
% Renter Occupied (10-year change) Point change
% Renter Occupied (5-year change) Point change
% Renters Spending 50%+ of Income on Rent (10-year change) Point change
% Renters Spending 50%+ of Income on Rent (5-year change) Point change
% Self-Employed (10-year change) Point change
% Self-Employed (5-year change) Point change
% Single-Family Homes (10-year change) Point change
% Single-Family Homes (5-year change) Point change
% Taking Public Transit to Work (10-year change) Point change
% Taking Public Transit to Work (5-year change) Point change
% Under 18 (10-year change) Point change
% Under 18 (5-year change) Point change
% Unemployed (of Civilian Labor Force) (10-year change) Point change
% Unemployed (of Civilian Labor Force) (5-year change) Point change
% Veterans (Age 18+) (10-year change) Point change
% Veterans (Age 18+) (5-year change) Point change
% Walking or Biking to Work (10-year change) Point change
% Walking or Biking to Work (5-year change) Point change
% With Bachelor's or Higher (10-year change) Point change
% With Bachelor's or Higher (5-year change) Point change
% With Graduate or Professional Degree (10-year change) Point change
% With Graduate or Professional Degree (5-year change) Point change
% With No High School Diploma or GED (10-year change) Point change
% With No High School Diploma or GED (5-year change) Point change
% Without Health Insurance (10-year change) Point change
% Without Health Insurance (5-year change) Point change
% Working From Home (10-year change) Point change
% Working From Home (5-year change) Point change
% Working in Construction (10-year change) Point change
% Working in Construction (5-year change) Point change
% Working in Food Service, Arts or Accommodation (10-year change) Point change
% Working in Food Service, Arts or Accommodation (5-year change) Point change
% Working in Health Care or Education (10-year change) Point change
% Working in Health Care or Education (5-year change) Point change
% Working in Manufacturing (10-year change) Point change
% Working in Manufacturing (5-year change) Point change
% Working in Professional or Business Services (10-year change) Point change
% Working in Professional or Business Services (5-year change) Point change
% Working in Retail Trade (10-year change) Point change
% Working in Retail Trade (5-year change) Point change
Average Household Size (10-year change) Value difference
Average Household Size (5-year change) Value difference
Households (10-year change) Percent change
Households (5-year change) Percent change
Housing Units (10-year change) Percent change
Housing Units (5-year change) Percent change
Population (10-year change) Percent change
Recent Population Growth Percent change

ACS change with tract sources (22 maps)

Reads the current tract endpoint directly, reallocates the historical tract endpoint to 2022 boundaries, then compares them.

% Below Poverty Level (10-year change) Point change
% Below Poverty Level (5-year change) Point change
% Enrolled in College or Graduate School (10-year change) Point change
% Enrolled in College or Graduate School (5-year change) Point change
% Enrolled in K-12 (10-year change) Point change
% Enrolled in K-12 (5-year change) Point change
% Foreign-Born (10-year change) Point change
% Foreign-Born (5-year change) Point change
% Households With 2+ Workers (10-year change) Point change
% Households With 2+ Workers (5-year change) Point change
% Households: No Vehicle Available (10-year change) Point change
% Households: No Vehicle Available (5-year change) Point change
% Living in Group Quarters (10-year change) Point change
% Living in Group Quarters (5-year change) Point change
% Speaking a Non-English Language at Home (5-year change) Point change
% Speaking English Less Than "Very Well" (5-year change) Point change
% Who Moved in the Past Year (10-year change) Point change
% Who Moved in the Past Year (5-year change) Point change
% With a Disability (10-year change) Point change
% With a Disability (5-year change) Point change
Mean Commute (Minutes) (10-year change) Value difference
Mean Commute (Minutes) (5-year change) Value difference

2020 Census population density (1 map)

Divides 2020 Census population by 2020 land area for each 2022 tract.

Population Density Rate

Day and night population shift (1 map)

Subtracts Census LEHD LODES residence jobs from workplace jobs and divides the result by 2020–2024 ACS population. Alaska uses 2016 LODES data, Michigan uses 2021, and every other state and DC uses 2023.

Day and night population shift Rate

Why historical maps use current boundaries

BlockAtlas has a limited set of display levels for national maps. These levels do not yet include historical tracts or block groups, so BlockAtlas reallocates historical data to current boundaries for display.