Zip code of usa wikipedia

In fact, they're only 52 years old—a concept that was introduced during World War II, and officially implemented in The zip Zoning Improvement Plan code was created when the postal service lost a huge portion of their staff who went to fight in the war.

Because of this, they needed a simple way to help the understaffed postal service deliver mail effectively. Initially, the zip code was only a two-digit number: the first denoted the city, the second denoted the state. But as the need for delivery expanded, so did the concept of the zip code.

As of , zip codes' numbers are determined by a few factors: the area, the regional postal facility and the local zone. The first number of the five-digit code signifies the region which the address is located in, a number that grows from the east coast to the west. For example, Eastern states such as Maine and New York begin with 0 or 1, whereas the Western states of California and Washington begin with a 9. The second two digits in the code determine a smaller region within each initial area that translates to a central post office facility for that area.

The final two digits signify the local post office of the address. 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. Very rural areas aren't labeled as belonging to a ZIP code such as much of Nevada and Utah where there are few, if any, addresses to deliver mail.

If the address is on the same street as a ZIP code boundary on the map, be sure to search for the full street address to determine the ZIP code instead of relying on the map. Their purpose is to convey statistical data about regions that are familiar to most citizens. As discussed above, it is difficult to precisely define a geographic area covered by a ZIP code.

ZCTAs were developed to account for some of the difficulties in assigning an area to a ZIP code and to precisely define a geographic area. In general, they are updated once every 10 years for the Census. The Census assigns an area to a ZCTA according to census blocks the smallest geographic unit used by the census.

Imagine a city block that makes up a typical census block as pictured to the right. It is bounded on all 4 sides by portions of city streets that each have their own name and addresses. The issue is that census blocks almost always split down the middle of the street. ZIP codes rarely do because that would require two postal workers delivering mail to that street - one for each side of the street. In the example, one mail carrier may deliver to 3 sides of the block via one ZIP code while another mail carrier delivers mail on the other street in a different ZIP code.