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Working with ZIP code data (and alternatives to using sketchy ZIP code data)

1711 North Kimball Avenue, built 1890

This building at 1711 N Kimball no longer receives mail and the local mail carrier would mark it as vacant. After a minimum length of time the address will appear in the United States Postal Service’s vacancy dataset, provided by the federal Department of Housing and Urban Development. Photo: Gabriel X. Michael.

Working with accurate ZIP code data in your geographic publication (website or report) or demographic analysis can be problematic. The most accurate dataset – perhaps the only one that could be called reliably accurate – is one that you purchase from one of the United States Postal Service’s (USPS) authorized resellers. If you want to skip the introduction on what ZIP codes really represent, jump to “ZIP-code related datasets”.

Understanding what ZIP codes are

In other words the post office’s ZIP code data, which they use to deliver mail and not to locate people like your publication or analysis, is not free. It is also, unbeknownst to many, a dataset that lists mail carrier routes. It’s not a boundary or polygon, although many of the authorized resellers transform it into a boundary so buyers can geocode the location of their customers (retail companies might use this for customer tracking and profiling, and petition-creating websites for determining your elected officials).

The Census Bureau has its own issues using ZIP code data. For one, the ZIP code data changes as routes change and as delivery points change. Census boundaries needs to stay somewhat constant to be able to compare geographies over time, and Census tracts stay the same for a period of 10 years (between the decennial surveys).

Understanding that ZIP codes are well known (everybody has one and everybody knows theirs) and that it would be useful to present data on that level, the Bureau created “ZIP Code Tabulation Areas” (ZCTA) for the 2000 Census. They’re a collection of Census tracts that resemble a ZIP code’s area (they also often share the same 5-digit identifiers). The ZCTA and an area representing a ZIP code have a lot of overlap and can share much of the same space. ZCTA data is freely downloadable from the Census Bureau’s TIGER shapefiles website.

There’s a good discussion about what ZIP codes are and aren’t on the GIS StackExchange.

Chicago example of the problem

Here’s a real world example of the kinds of problems that ZIP code data availability and comprehension: Those working on the Chicago Health Atlas have run into this problem where they were using two different datasets: ZCTA from the Census Bureau and ZIP codes as prepared by the City of Chicago and published on their open data portal. Their solution, which is really a stopgap measure and needs further review not just by those involved in the app but by a diverse group of data experts, was to add a disclaimer that they use ZCTAs instead of the USPS’s ZIP code data.

ZIP-code related datasets

Fast forward to why I’m telling you all of this: The U.S. Department of Housing and Urban Development (HUD) has two ZIP-code based datasets that may prove useful to mappers and researchers.

1. ZIP code crosswalk files

This is a collection of eight datasets that link a level of Census geography to ZIP codes (and the reverse). The most useful to me is ZIP to Census tract. This dataset tells you in which ZIP code a Census tract lies (including if it spans multiple ZIP codes). HUD is using data from the USPS to create this.

The dataset is documented well on their website and updated quarterly, going back to 2010. The most recent file comes as a 12 MB Excel spreadsheet.

2. Vacant addresses

The USPS employs thousands of mail carriers to delivery things to the millions of households across the country, and they keep track of when the mail carrier cannot delivery something because no one lives in the apartment or house anymore. The address vacancy data tells you the following characteristics at the Census tract level:

  • total number of addresses the USPS knows about
  • number of addresses on urban routes to which the mail carrier hasn’t been able to delivery for 90 days and longer
  • “no-stat” addresses: undeliverable rural addresses, places under construction, urban addresses unlikely to be active

You must register to download the vacant addresses data and be a governmental entity or non-profit organization*, per the agreement** HUD has with USPS. Learn more and download the vacancy data which they update quarterly.

Tina Fassett Smith is a researcher at DePaul University’s Institute of Housing Studies and reviewed part of this blog post. She stresses to readers to ignore the “no-stat” addresses in the USPS’s vacancy dataset. She said that research by her and her colleagues at the IHS concluded this section of the data is unreliable. Tina also said that the methodology mail carriers use to identify vacant addresses and places under change (construction or demolition) isn’t made public and that mail carriers have an incentive to collect the data instead of being compensated normally. Tina further explained the issues with no-stat.

We have seen instances of a relationship between the number of P.O. boxes (i.e., the presence of a post office) and the number of no-stats in an area. This is one reason we took it off of the IHS Data Portal. We have not found it to be a useful data set for better understanding neighborhoods or housing markets.

The Institute of Housing Studies provides vacancy data on their portal for those who don’t want to bother with the HUD sign-up process to obtain it.

* It appears that HUD doesn’t verify your eligibility.

** This agreement also states that one can only use the vacancy data for the “stated purpose”: “measuring and forecasting neighborhood changes, assessing neighborhood needs, and measuring/assessing the various HUD programs in which Users are involved”.

Finding teardowns in Chicago

1923 South Allport Avenue, built 1884

A recent suspected teardown, at 1923 S Allport in Pilsen (25th Ward, 19th place for teardowns from 2006 to now). The demolition permit was issued August 7 and the new construction permit was issued August 5. The new building will have an increase in density, with three dwelling units. Photo by Gabriel Michael.

From Wikipedia, a teardown is a “process in which a real estate company or individual buys an existing home and then demolishes and replaces it with a new one”.

You can find suspected* teardowns in the building permits data on Licensed Chicago Contractors by looking for demolition permits and new construction permits for the same address. I limited my search to situations where the demolition permit was issued within 60 days prior or subsequent to the new construction permit. This shows properties that have a quick turnaround (thus more likely to get built). I didn’t want to include buildings that may have been demolished one year and got a building two years later.

Analysis

This analysis is based on data since January 1, 2006, the start of the first complete year of building permits data in the Chicago open data portal, and ends today. The first demolition permit in this analysis was issued January 10, 2006, and its associated new construction permit was issued five days prior. There may be a case when the demolition permit and new construction permits were issued in different years, but for this analysis I only consider the year in which the demolition permit was issued. (In my review of permits since March I believe that new construction permits are issued most often after the demolition permit.)

Suspected teardowns

The number for teardowns decreased dramatically as the economic crisis approached.

Results

There were 1,717 suspected teardowns in Chicago distributed across 57 community areas (of 77, whose boundaries don’t change) and 45 wards (of 50, whose boundaries changed in 2012).

West Town, Lake View, and North Center share top billing, with the most teardowns each year, but Lake View was #1 for seven of 10 years. Other top five community areas comprise Logan Square (thrice), Lincoln Square (thrice), Bridgeport (twice), McKinley Park (once), and Near West Side (once).

From 2012 to current, the most teardowns occurred in Wards 32 (Waguespack), 47 (Pawar), 1 (Moreno), 44 (Tunney), and 43 (Smith). All of those wards include parts of the top three community areas mentioned above.

The sixth ward with the most teardowns in this period was 2 (Fioretti) but this boundary no longer represents any part of the pre-2012 boundary that covered almost the entire South Loop. That means Ward 2 is now covering the west side. Additionally, the 2nd Ward made sixth place with 28 teardowns and fifth place, the 43rd Ward had 60 teardowns.

The South Loop, represented by the Near South Side community area, has had 0 suspected teardowns from 2012 to now. There was one teardown in the entire time period, where a three-story commercial was demolished at 1720 S Michigan Ave and replaced with a 32-story residential tower.

What else do you want to know about teardowns in Chicago?

* Notes

I use “suspected” because it’s impossible to know from the data if buildings were actually demolished and constructed.

Download the data as CSV for yourself.

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