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. The city is usually the name of the main post office. The Census assigns an area to a ZCTA according to census blocks the smallest geographic unit used by the census. Portland, Oregon Zip Code: 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. With ZipCodeDownload there is no need to wait For the mail and pay shipping costs for your zip code database. When we say that our data is available for immediate download, we mean it!
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The additional 4 digits help USPS more precisely group mail for delivery. 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: 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.
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