Reading a ZIP Code: What Each Digit Tells You

## The Geographic Code

Every ZIP code is a geographic breadcrumb trail. By reading it digit by digit, you can determine the region, state, and approximate area of an address without looking it up.

## First Digit: National Region

The United States is divided into 10 ZIP code regions:

| Digit | Region | States |
|-------|--------|--------|
| 0 | Northeast | CT, MA, ME, NH, NJ, NY, PR, RI, VT, VI |
| 1 | Northeast | DE, NY, PA |
| 2 | Mid-Atlantic | DC, MD, NC, SC, VA, WV |
| 3 | Southeast | AL, FL, GA, MS, TN |
| 4 | Great Lakes | IN, KY, MI, OH |
| 5 | Upper Midwest | IA, MN, MT, ND, SD, WI |
| 6 | Central | IL, KS, MO, NE |
| 7 | South Central | AR, LA, OK, TX |
| 8 | Mountain West | AZ, CO, ID, NM, NV, UT, WY |
| 9 | Pacific | AK, CA, HI, OR, WA |

## Second and Third Digits: SCF

The second and third digits identify the Sectional Center Facility (SCF) — a large mail processing hub. Each SCF serves a cluster of post offices. For example:

- **100** = New York, NY (Manhattan SCF)
- **606** = Chicago, IL (South Suburban SCF)
- **900** = Los Angeles, CA (LA SCF)

There are approximately 900 SCFs across the country.

## Fourth and Fifth Digits: Delivery Zone

The last two digits identify a specific post office or delivery zone within the SCF area. Lower numbers are generally assigned to the main post office in a city, with higher numbers going to surrounding towns and suburbs.

## Patterns to Notice

- ZIPs increase roughly from east to west and north to south
- State capitals often have ZIPs ending in 01 (e.g., 04101 = Augusta, ME; but not always)
- Large cities span many ZIP codes: New York uses 10001-10292, Los Angeles uses 90001-90089
- Gaps in the sequence exist where ZIPs have been retired

## Practical Applications

Knowing how to read a ZIP code helps with quick geographic estimation, data validation (a ZIP starting with 9 should be in a Pacific state), and understanding USPS routing logic.