Zip county

In these files the denominators used to calculate the address ratios are the ZIP code totals. All three files share an identical structure with the exception of the geographic codes in the second column, which differs between the three crosswalk files — tract, county, and CBSA — respectively.

In the example below, ZIP code is split by two different Census tracts, and , which appear in the tract column. The remaining residential addresses in that ZIP So, for example, if one wanted to allocate data from ZIP code to each Census tract located in that ZIP code, one would multiply the number of observations in the ZIP code by the residential ratio for each tract associated with that ZIP code. Note that the sum of each ratio column for each distinct ZIP code may not always equal 1.

The decimal is implied and leading and trailing zeros have been preserved. In these files the denominators used to calculate the address ratios are the totals of each type of address in the tract, county or CBSA. All three files share an identical structure with the exception of the geographic codes in the first column, which differs between the three crosswalk files — CBSA, County, and Tract — respectively.

In the example below tract is split by two different ZIP codes, and , which appear in the ZIP column. The ratio of residential addresses in the first tract-ZIP record to the total number of residential addresses in the tract is.

The remaining residential addresses in that tract So, for example, if one wanted to allocate data from Census tract to the ZIP code level, one would multiply the number of observations in the Census tract by the residential ratio for each ZIP code associated with that Census tract. Since the HUD geocoding base map is updated regularly, an effort is made to re-geocode these records with every new quarter of data.

As a result, these crosswalk files will be generated on a quarterly basis and may differ slightly from quarter to quarter. We try to publish the Crosswalk Files by the end of the month following the quarter. For example, we aim to publish fourth quarter by the end of January, first quarter by the end of April, and so on. Do ZIP Codes align with political or administrative boundaries? ZIP Codes do not align with political or administrative boundaries.

ZIP Codes frequently cross county, city, and town jurisidctions. ZIP Codes may also potentially cross state borders. ZIP Codes have the potential to intersect with multiple geographies. The ratio fields describe the percentage of the respective addresses that fall in both that ZIP Code and each county. As addresses are created or removed, this changes the ratios in the associated geographies.

Why is there a large jump in the number of addresses from to ? Many students also use the files. 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. 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.