Otherwise, you may wind up concluding that there has been a dramatic downward trend in the population of 63301 since 1980, when in fact just the opposite is true. What this means, of course, is that ZIP codes are really terrible units for doing any kind of time-series analysis unless you have some way of keeping track of all the changes over time. The new code 63303 did not exist in 1985 and it has already changed its definition so that it now represents about half of the area it included when it was initially created (by splitting 63301 into 6333 a few years later the initial 63303 ZIP was subdivided into 6334.). So what is referred to as 63301 today represents about a third of the area that it referred to in 1985. Charles county, Mo in 1985 was subsequently broken into first two and then three ZIP codes. The ZIP code that was called '63301' in St. When a ZIP codes changes its definition it does not change its name like a census tract. In some cases these changes can be quite dramatic, but more commonly they are small and subtle. How ZIP Codes Change Over TimeĪn important thing to keep in mind about ZIP codes is that they change over time. If you have an application that requires extreme geographic precision, especially in sparsely populated areas, then you need to avoid using ZIP codes. So the actual definition of a ZIP code "boundary" is quite fuzzy at best, and a purely extrapolated guess (at what it would be if someone were to start receiving mail there) at worst. until there needs to be mail delivered there. An area will not be assigned a ZIP code until there is a reason for it, i.e. You may see maps that show ZIP code boundaries that include such areas, but these are not post-office-defined official definitions. In areas where there is no mail delivery (deserts, mountains, lakes, much of Nevada and Utah) ZIP codes are not really defined. In rural areas, ZIP codes can be collections of lines (rural delivery routes) that in reality do no look much like a closed spatial area. As such, ZIP codes do in most cases resemble spatial areas since they are comprised of spatially clustered street ranges. They are simply categories for grouping mailing addresses. Postal Service, ZIP codes are not and never have been such spatial entities. But, from the perspective of the agency that defines them, the U.S. We see maps of ZIP codes in telephone books and from commercial vendors that make us think of them as spatially defined areas with precise boundaries, similar to counties. Because it is an acronym we always use the uppercase for it.) ZIP codes have been adopted by marketing people and by all kinds of other researchers as a standard geographic area, like a city or a county. ("ZIP" is actually an acronym for "Zone Improvement Plan", where "Zone" is a reference to the 2-digit postal zones that were used by the post office prior to implementing nationwide ZIP codes back in the early 1960's. Postal Service as a tool to help deliver the mail more efficiently. ZIP codes are a very messy kind of geography. General Information and Problems with ZIP Codes Problems With Spatial Definition We place special emphasis on tools for linking ZIP (/ZCTA) codes to other geographies (such as counties, cities, metro areas) and to demographic information from the latest decennial census. This version focuses on the Census Bureau's 2000 vintage ZIP Census Tabulation Areas (ZCTAs), close cousins of ZIP codes. It provides some general background information about ZIP codes and describes and links to various reference materials, data files, web sites, and other resources of interest to users wanting to work with ZIPs.
This page serves as a guide for researchers interested in U.S. All about ZIP Codes The ZIP Code Resources Page
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