What is an address?

Addresses help us navigate our lives. Their infrastructure lets us identify a location, and specify where a place is— even if we’ve never been there. But, what is an address? Addresses are made up of simple and straightforward components that can be leveraged to enhance our understanding of a location. The level of knowledge that an address gives varies by country, as countries have implemented different infrastructures.

Addresses within Mannheim, Germany’s historic district are set on a separate grid from the rest of the city, and defined based on their distance from the city center. Japanese addresses detail every city blocks history, as street names and unit numbers are issued in chronological order. In the United States, addresses can be used to determine if a location is currently occupied, in a region where people work or live, and identify what sales tax rate applies.

Every US address contains deeper insights beyond its location. But what happens when insights are drawn from all the addresses rather than just one? What insights can we learn from all of the address in America?

To celebrate our billionth address verification, we’re sharing our findings with you.

Before we dive into metrics, let’s get some small housekeeping items out of the way:

A typical street address is on two to three lines and includes a primary unit number, street name and suffix, city, state, and zip code.

Some streets need additional directional information. If these are included before the street name, they are called predirectionals. If the directional information follows the street name, it’s called a postdirectional.

Many addresses also have secondary unit information, which indicate if the address is in a multi-unit complex such as an apartment building or office complex. This information can be written on a separate line from the primary address information, however, USPS standard formatting has it on the first line.

A secondary unit information consists of a secondary unit designator (like Apt., Suite, Dept.) and a secondary unit number.

While there is no national standard for how primary unit numbers are organized in the US, our data suggests that cities tend to use a consistent logic. Generally, primary unit numbers on a street consistently increase or decrease in a directional order with even and odd numbers being on the opposite sides.

Primary unit numbers are usually not consecutive. This results in some primary unit numbers being more popular than others. For example, we frequently see multiples of five.

These figures also highlight some of our cultural norms. 13 is perceived to be an unlucky number, and there is a sharp decline for number of addresses that utilize it. There are roughly twice as many addresses that utilize the primary unit 15 over 13.

If we zoom out, we can see that these patterns repeat. A common city planning strategy is to have every block represent a value of 100 primary unit, which makes it easier for individuals to navigate.

Most cities determine a few baselines from where these numbers originate. When using a map that identifies these baselines (by looking at the density of primary unit number 1), we can identify areas of interest in cities.

San Francisco is a city that is set with against several different grids, all of which converge in unique ways. San Francisco’s main thoroughfare, Market Street, is a baseline for the neighboring streets that lie north and south of it. There is a higher concentration along the city of San Francisco’s borders, except for the northern border, where parks are located.

Currently, city councils approve street names which are submitted by real estate developers. There is no uniform criteria that city councils consider before approving a street name. However, there are insights and trends that tell a story for what city planners tend to favor.

Some of the most popular names are numbers, however, the most common street name is Main.

There are more Second street names than First street names. It’s possible that First street names have been renamed or that the naming convention used has skipped First.

After numbers, popular themes tend to emerge which give insights into our culture and identify high commerce areas and important historical figures.

Main is the most popular name for roadways in America, and is frequently used to designate commercial areas. Front and High designate commercial areas in other countries, which could explain their popularity in the US.

Natural resources are a popular theme and have some of the most common names.

Important historical figures is also a popular theme. By looking at these names, we can infer important figures in our country’s history.

...and we’ve also found the theme of words found in the Constitution and Declaration of Independence.

Historically, the characteristics of a road would define it’s suffix, which is why you can identify a freeway from an alley. The makings of each suffix allow us to understand the intention of each street.

Nearly 20% of Americans live in apartment buildings, and while the apartment might be our most popular type of designator for secondary unit information— it's far from the only one. There are 24 secondary unit designators that range in popularity. Here you can see how popular each designator is.

The first multi-story building was built in the city of Çatalhöyük around 7500 BCE. In 1884, architects in Chicago built the first skyscraper. Today, our data indicates that only 12.1% of addresses contain a secondary unit designator.

The use of secondary units is less regulated than primary unit numbers. If you were to add secondary units to an address, you’d need to submit floor plans to local city and county planning departments, which allows USPS to track when secondary units can start accepting mail.

Using numbers to identify regions beyond city and state originated back in 1943, when post office codes were introduced to help reduce the operational impact of sorting mail. However, it didn’t take long for us to outgrow these two digit codes.

Robert Moon expanded these codes, to create the Zone Improvement Program which was implemented in 1963 by the USPS. The system leveraged the previous coding system, leaving them as the last two digits as they expanded ZIP codes to include an additional three digits that convey additional information.

When looking at the digits of the ZIP code, we can identify various specific regions.

The first number identifies a broad area (like West coast).

The next two numbers identify a more specific area (like a state or a region). The first three numbers correlate to a central mail processing facility, which processes all mail with the same first three digits.

The last two digits identify a city or a regional post office code.

ZIP codes were implemented to expedite the delivery of mail, and follow the patterns of mail routes, which means they can follow unusual patterns that make them difficult to put cleanly on a map. They weren't made to correspond to existing boundaries such as cities, counties, or even states. Additionally, the USPS updates ZIP codes quarterly. While it’s rare for existing ZIP codes to change, it can happen to accommodate a new post office opening or an old post office closing.

The ZIP +4 was introduced in 1983 and further identifies more specific regions:

The 6 + 7 digits identify a delivery sector.

The last two digits are a delivery segment, sometimes being a department in an office or PO box.