Why is zip code X missing? Or what is a ZCTA, and how is it different from a zip code?

Since the demographic data on this website is from the US Census Bureau, we’re using the US Census Bureau’s ZIP Code Tabulation Areas (ZCTAs), which are generalized areal representations of United States Postal Service ZIP Code service areas.

A zip code is technically a linear postal route. I like to imagine zip codes as a postman driving in a line, up and down streets, delivering mail. Here’s a fun animation about how the Census Bureau turns linear routes into polygons: 

Sometimes, there isn’t a ZCTA for a "weird" zip code. The most common example of "weird" zips are PO Box zips (so zips of only businesses and no residents, and you need residents for demographic estimates). Other weird zips that we’ve run into in the past include a zip only for the IRS or a post office. Lastly, sometimes, there aren't enough samples in a zip/ZCTA to produce an estimate (aka too few people living in the zip).

On this website, we use the terms ZCTA, zip code or zip interchangeably. Most people who we work with don’t know what a ZCTA is and the difference between a zip code and ZCTA doesn’t impact how they need to use the data. Of course, theoretical problems could arise with using ZCTAs if you are doing a mailing list or mass mail project.

What to do if you HAVE to have demographics for a zip that doesn't have a ZCTA?

Check out this handy zip to ZCTA crosswalk.

How Could You Use This Crosswalk?

Let’s say you were asked to rank a list of addresses from most likely to buy to least likely to buy. Since this is a quick test to see if using demographic data will improve your close rate, you are going to simply associate each lead with some basic demographics for the zip, for instance, median household income. 90% of your addresses have zips that match ZCTAs, so it’s easy to match these leads with their ZCTA demographics. But the remaining 10% of your addresses don’t have a matching ZCTA. You could then use the above crosswalk to associate the weird zips with a ZCTA, and thus, pull demographics for the rest of your addresses.

Got more zip/ZCTA questions? Contact us.

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