Census Blocks
Contents
A census block is the smallest geographic unit for which the U.S. Census Bureau collects and tabulates data. Think of them as the building blocks of all other census geographies, such as block groups, census tracts, counties, and states.
Here are some key characteristics of census blocks:
| • | Boundaries: Blocks are defined by both visible and non-visible features. |
| o | Visible features: These include streets, roads, streams, railroad tracks, and shorelines. |
| o | Non-visible boundaries: These can be political boundaries like city, township, school district, or county limits, as well as property lines. |
| • | Size and Population: While a census block in an urban area may correspond to a typical city block bounded by streets, blocks in rural areas can be much larger, covering many square miles. Consequently, the population of a census block can range from zero to several hundred people. |
| • | Data Availability: The Census Bureau releases "100-percent data" at the block level. This refers to the basic demographic data collected from every household, such as total population by age, sex, and race. However, for more detailed "sample data" collected from a fraction of the population (like that from the American Community Survey), the smallest geographic unit available is the census block group, which is a cluster of blocks. |
| • | Unique Identification: Every census block in the country has a unique 15-digit code that is a combination of its state, county, census tract, and block codes. |
| • | Usefulness: Census blocks are crucial for many purposes, including: |
| o | Redistricting: Legislative and voting districts are created by combining census blocks. |
| o | Urban planning and research: Planners and researchers use block-level data to analyze population distribution, housing patterns, and other trends at a fine-grained level. |
| o | Emergency services: Knowing the population density of a census block can help in planning for emergency response. |