MSAs and CBSAs: Metro Area Definitions
Metropolitan statistical areas group counties around urban cores. Learn how MSAs and CBSAs relate to ZIP codes.
## What Are MSAs?
A Metropolitan Statistical Area (MSA) is a geographic region defined by the Office of Management and Budget (OMB) around an urban core of 50,000+ population, plus surrounding counties with strong commuting ties.
MSAs are the standard unit for analyzing urban economies, housing markets, and labor markets.
## MSA vs. CBSA
Core Based Statistical Areas (CBSAs) include both MSAs and smaller Micropolitan Statistical Areas:
| Type | Core Population | Count (2023) |
|------|----------------|---------------|
| Metropolitan (MSA) | 50,000+ | 384 |
| Micropolitan (µSA) | 10,000-49,999 | 543 |
| Combined (CSA) | Linked MSAs/µSAs | 175 |
## Largest MSAs
| Rank | MSA | Population | ZIP Codes |
|------|-----|------------|----------|
| 1 | New York-Newark-Jersey City | 19.8M | ~2,400 |
| 2 | Los Angeles-Long Beach-Anaheim | 13.0M | ~1,200 |
| 3 | Chicago-Naperville-Elgin | 9.4M | ~900 |
| 4 | Dallas-Fort Worth-Arlington | 7.6M | ~600 |
| 5 | Houston-The Woodlands-Sugar Land | 7.1M | ~500 |
## MSA-ZIP Relationship
MSAs are defined by counties, and counties contain multiple ZIP codes. Therefore:
- Every ZIP within an MSA county is considered part of that MSA
- ZIP codes that span MSA-boundary counties get assigned to the MSA with the higher residential ratio
- Non-MSA ZIPs are classified as "non-metropolitan" or rural
## Why MSAs Matter
MSAs are used everywhere in economic analysis:
- **Bureau of Labor Statistics** — Unemployment rates by MSA
- **Federal Reserve** — Banking and economic data by MSA
- **HUD** — Fair market rents and housing affordability by MSA
- **Media markets** — Nielsen DMAs roughly align with MSAs
- **Corporate planning** — Market sizing, store placement, hiring
## MSA Boundary Changes
OMB periodically revises MSA definitions. The most recent major revision (2023) changed the minimum population threshold for MSAs and reclassified dozens of areas. These changes affect federal funding, statistical comparisons, and business analytics.