About Us
What is BlockAtlas?
BlockAtlas lets you view geographic territories and make choropleth maps of them. Territories can be standard census geographies (states, counties, cities, tracts) or custom boundaries you upload. Data can come from the U.S. Census, your own CSV files, or properties embedded in your GeoJSON.
Map types
Every map on BlockAtlas is a choropleth: each region is assigned a value (or two), which determines its color. Options include:
- Flat — a base choropleth
- 3D extrusion — height encodes an additional variable
- Bivariate — two variables mapped to a 2D color legend
- Multi-map — up to 8 maps side by side
Data sources
- American Community Survey — 1-year and 5-year estimates
- Decennial Census — 2020 population counts
- CSV upload — your data, keyed by GEOID
- GeoJSON upload — custom territories with optional data properties (see below)
Custom territories
GeoJSON uploads define arbitrary boundaries—school districts, sales regions, neighborhoods, etc. Census data is then aggregated to these custom areas.
How aggregation works
Census geography: The Census Bureau divides the U.S. into tracts (typically with a few thousand people each) and blocks (the smallest unit, bounded by streets or other features).
Boundary mismatch: Custom territories rarely align with tract boundaries. We compute what fraction of each tract's population falls within your territory using block-level intersection.
Aggregation method:
- Counts/totals (e.g., population) — weighted sum
- Rates/medians/indices (e.g., median income) — weighted average
This is experimental. Results may differ from official statistics. We ask you to specify whether each indicator is a count or a rate so we can aggregate correctly.
Geographic levels
Maps can display data at the state, county, city, or tract level.
Place explorer
The place explorer lets you browse census geographies and any custom territories you've uploaded. Select a place to see its boundaries and a demographic overview pulled from the Census API. For custom territories, this overview uses the aggregation methods described above.
Sharing
Maps can be published to the public gallery or kept private.