Statistical Areas of the United States
To accurately track population clusters and economic trends, the Office of Management and Budget (OMB) has designated more than 1,000 statistical areas across the United States and Puerto Rico. These geographic delineations serve as critical tools for the US Census Bureau, planning organizations, and various levels of government to analyze social and economic integration.
Defining Core-Based Statistical Areas (CBSA)
A Core-based Statistical Area (CBSA) is defined as a county or counties (or county-equivalents) that surround at least one densely settled core with a population of at least 10,000. To be included in a CBSA, adjacent counties must demonstrate a high degree of social and economic integration with the core, which is primarily measured through commuting ties.
The OMB further categorizes CBSAs into two types based on their population size:
- Metropolitan Statistical Area (MSA): An area with a population of at least 50,000.
- Micropolitan Statistical Area (μSA): An area with a population ranging from 10,000 to 49,999.
Advanced Statistical Classifications
Beyond the basic CBSA, the OMB utilizes broader classifications to capture larger regional connections:
Combined Statistical Areas (CSA)
A Combined Statistical Area (CSA) consists of two or more adjacent CBSAs. The primary requirement for this designation is an employment interchange rate of at least 15%, which is calculated by adding the percentage of people commuting from area A to B and from area B to A.
Primary Statistical Areas (PSA)
A Primary Statistical Area (PSA) is a comprehensive designation that includes all CSAs as well as any CBSA that does not belong to a combined statistical area.
Key Facts
- The OMB manages over 1,000 statistical areas for the US and Puerto Rico.
- A CBSA requires a core population of at least 10,000.
- MSAs have 50,000+ people, while μSAs have between 10,000 and 49,999.
- CSAs are formed when adjacent CBSAs have an employment interchange rate of 15% or higher.
Maine Statistical Data Analysis
Using the state of Maine as an example, we can see how these designations apply to real-world populations. The state's total estimated population for 2025 is 1,414,874.
| Combined Statistical Area (CSA) | Core-based Statistical Area (CBSA) | County | Population (2025 Est.) |
|---|---|---|---|
| Portland–Lewiston–South Portland, ME CSA | Portland–South Portland, ME MSA | Cumberland County | 317,222 |
| Portland–Lewiston–South Portland, ME CSA | Portland–South Portland, ME MSA | York County | 222,434 |
| Portland–Lewiston–South Portland, ME CSA | Portland–South Portland, ME MSA | Sagadahoc County | 37,979 |
| Portland–Lewiston–South Portland, ME CSA | Lewiston–Auburn, ME MSA | Androscoggin County | 116,487 |
| None | Bangor, ME MSA | Penobscot County | 157,967 |
| None | Augusta–Waterville, ME μSA | Kennebec County | 129,607 |
Population Trends in Maine's Top Areas
The Portland–South Portland MSA remains the most populous area, showing steady growth from 514,098 in 2010 to an estimated 577,635 in 2025. Similarly, the Portland–Lewiston–South Portland CSA has grown from 621,800 in 2010 to an estimated 694,122 in 2025.
Frequently Asked Questions
What is the difference between an MSA and a μSA?
The difference is based on population size: a Metropolitan Statistical Area (MSA) must have at least 50,000 people, whereas a Micropolitan Statistical Area (μSA) has a population between 10,000 and 49,999.
How is a Combined Statistical Area (CSA) determined?
A CSA is formed when two or more adjacent CBSAs have an employment interchange rate (the sum of commuting percentages between the areas) of at least 15%.
What is a Primary Statistical Area (PSA)?
A PSA is a broad category that encompasses all Combined Statistical Areas (CSAs) and any Core-based Statistical Area (CBSA) that is not part of a CSA.
Who is responsible for designating these statistical areas?
The Office of Management and Budget (OMB) is the entity responsible for designating these areas for the United States and Puerto Rico.