Mail carriers even know when houses in Truth or Consequences, N.M., go vacant. Lucy Nicholson/Reuters

The U.S. Postal Service compiles information on every address in the country almost every day. Here's what they do with the numbers.

When they're not delivering mail or being bitten by dogs, U.S. Postal Service workers serve a third function: They collect property data on virtually every address in the nation. This service might be the postal worker's highest calling.

The Address Management System is a dataset compiled by USPS mail carriers and updated on the go as they perform their duties. Rain or shine, more than 307,000 mail carriers deliver mail to U.S. addresses nearly every day of the week. Mail carriers also compile parcel-level vacancy data to increase postal efficiencies, specifically by noting vacancies. These data help USPS clean up address lists that the agency provides to bulk mailers, among other things.

USPS sells change-of-address data to a variety of different companies. (Here's a good explanation for how this works.) But for privacy reasons, nobody-but-nobody outside the U.S. Census Bureau has access to USPS's entire big book of addresses. 

In 2004, however, the U.S. Department of Housing and Urban Development struck up a partnership that provides HUD with USPS's national address data in a format that still preserves the privacy of every address-holder in the nation. On a quarterly basis, USPS hands it over to HUD—in the form of ZIP+4 Code-level data aggregated to the 2010 U.S. Census Tract level.

"This is the most specific version of vacant data we make available, and only HUD is a recipient of this information," says USPS senior public relations representative Sue Brennan.

Geocoded at the Census Tract level, the data that USPS uses to clean up its national Rolodex can tell us broader things about housing—specifically, where vacancies turn into blight. The Census Tract level is a large enough locality to describe an area without revealing anyone's private information. 

"It’s administrative data," says Todd Richardson, associate deputy assistant secretary for HUD's Office of Policy Development. "USPS collects it for their purpose, and we’re using it for not the intended purpose."

Once the data are geocoded to the Census Tract level (a proxy for neighborhoods), HUD shares the data with non-profit and research organizations who apply for access. The agency itself has used the data to fuel several research initiatives: for example, to track the recovery in the Gulf Coast following Hurricane Katrina by watching as vacant addresses came back online. 

"The potential power of these data is that they represent the universe of all addresses in the United States and are updated every three months," reads one HUD explainer on the dataset.

Mail carriers can denote properties as being either "vacant" or "no-stat." Mail carriers on urban routes mark a property as vacant once no resident has collected mail there for 90 days. Addresses are classified as "no-stat" for a variety of reasons. Addresses along rural routes that appear to be vacant for 90 days are labeled no-stat. So are addresses for properties that are still under construction, and urban addresses that the mail carrier decides are unlikely to be occupied again any time soon—meaning that both areas of high growth and severe decline may be labeled no-stat.  

The Institute for Housing Studies at DePaul University is one of the organizations that receives these long-term vacancy data. Sarah Duda, associate director for the Institute, says that the organization uses the long-term vacancy data to research patterns of blight in the Chicago area

It turns out that when properties are listed as vacant for 24 months, Duda says, the conditions associated with blight are usually apparent. When properties in a neighborhood reach 24 months of vacancy, several blight indicators usually arise: high levels of foreclosures as well as cash and business buyers. 

There's no better dataset for tracking blight in Chicago, Duda says. Chicago's data for building violations, for example, are skewed by the fact that multifamily buildings require more permits and inspections than single-family units. And 40 percent of calls to 311 in Chicago are duplicate requests.

"The USPS is uniquely situated in many ways to collect these data because there’s no other national entity that has workers on the ground visiting properties on a consistent basis," Duda writes in an email. "That said, the data they are collecting is on unoccupied addresses, rather than what the public might think of as blighted vacant properties. Therefore, it’s important to use caution when using these data to assess the vacancy issue across neighborhoods."

Buda and officials at HUD hasten to note that address data collected by USPS are not first and foremost long-term vacancy data—they're administrative data, captured for a totally different purpose. The data, especially the no-stat data, must be couched in context: The no-stat label can be applied to budding suburban subdivisions as well as urban properties in serious decline. For that reason, the data are mostly useful for comparisons of a single area over time, rather than comparisons between areas. It's largely up to the mail carrier's discretion how the no-stat label is applied—and it's applied in different ways by carriers on urban and rural routes.

"A 'no-stat' means the address is not counted in the carrier’s delivery statistics as a point-of-service. The assignment differs between rural or city carriers due to the way the different carrier types are paid," Brennan explains by email. "For a city carrier, a 'no-stat' indicates the existence of an address but the carrier has not commenced service to the address or the address is not delivered directly by the carrier"—in a gated community, for example. "For a rural carrier, a 'no-stat' indicates the address has not been delivered to in the past 90 days," meaning the address is excluded for the purposes of determining the rural carrier's pay.

So these housing data aren't perfect, or rather, as postal-address administrative data, they aren't perfectly usable for researchers. But they are more complete and in some applications more revealing than other housing datasets. And since HUD has only been aggregating these data since 2005, the data are under-used. The unsung work of the USPS is as national housing data courier.


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