National address and zip 4 browser

Software Developer. Latest Updates. Lease or purchase software from an outside vendor and convert their own lists. Subcontract their conversion through a service bureau. The map of the first digit of zip codes above shows they are assigned in order from the north east to the west coast. The first 3 digits of a ZIP code determine the central mail processing facility, also called sectional center facility or "sec center", that is used to process and sort mail.

All mail with the same first 3 digits is first delivered to the same sec center where it is sorted according to the last 2 digits and distributed to local post offices. The sec centers are not open to the public and usually do most sorting overnight.

As you can see from the map of the first 3 digits of zip codes , the digits after the first are also generally assigned from east to west.

In the map, 0 is closer to white and 9 is much more vivid. It's easy to follow the gradient across each of the zones even though there are a few exceptions such as the southwest tip of Georgia which uses 39XXX like central Mississippi. Despite the fact that ZIP codes seem to be geographic in nature, that wasn't their intended purpose. They are intended to group mail to allow the USPS to deliver mail more efficiently. Some ZIP codes will span multiple states in order to make mail routing and delivery more efficient.

In most cases, addresses in close proximity to each other are grouped in the same ZIP code which gives the appearance that ZIP codes are defined by a clear geographic boundary. However, some ZIP codes have nothing to do with geogaphic areas. When ZIP codes appear to be geographically grouped, a clear shape cannot always be drawn around the ZIP code because ZIP codes are only assigned to a point of delivery and not the spaces between delivery points. In areas without a regular postal route or no mail delivery, ZIP codes may not be defined or have unclear boundaries.

The main issue is discussed above: there simply isn't always a clear geographic boundary for a ZIP code. The Census Bureau and many other commercial services will try to interpolate the data to create polygons shapes using straight lines to represent the approximate area covered by a ZIP code, but none of these maps are official or entirely accurate.

They provide a very close approximation of the area covered by a ZIP code. You can easily notice some of the boundary issues when viewing our maps. They also released the ZIP Code jingle:. As the US population has increased and scattered since , it's been necessary to expand on the system, to make room for everybody and their dog. That's where the "plus 4" part comes in. We're getting ahead of ourselves, though, so let's start with the basics.

If you're mailing a letter from Boston to Seattle, the mail carrier in Massachusetts doesn't really care what the street address of the destination is. It's what you might call "outside his jurisdiction. A postal worker can only cover so much ground on a given day. And since the USPS has a standard of delivering in rain, sleet or snow, that rules out the possibility of doing the service of delivering in stages some today, some tomorrow.

That means that any given post office is only servicing what it can reach in a day. ZIP Codes reflect that. Typically, a ZIP Code is tied to a post office; by that we mean, every one of the latter has one of the former. You might think of ZIP Codes as a mailing address for a particular post office.

Some do handle more than one ZIP Code, but a one-on-one game plan is the norm. It's very important to note that ZIP Codes aren't "boundaries. They don't follow geographic or administrative boundary lines; they can cross city, county, or even state lines.