The first digit
The first digit of a five-digit ZIP Code identifies a broad region of the United States. The general numbering pattern moves across large areas of the country, but it is not a simple state-by-state index.
The next digits
The remaining digits progressively narrow postal routing areas. Their meaning is tied to the postal network and should not be interpreted as a precise latitude-longitude coordinate or a strict county identifier.
Why prefixes have limits
A prefix can provide a broad clue for sorting or exploratory analysis, but ZIP Code assignments can cross familiar geographic boundaries. Prefixes do not reliably identify a city, county, congressional district or state in every situation.
Use full records for decisions
When an exact location matters, use the complete ZIP Code and a validated street address. For statistical mapping, use an appropriate geographic dataset such as Census geography.