Tag: Census data

Determining dwelling unit count at an address using 1950 Census records

March 11, 2023 / / 0 Comments

It’s possible to use 1950 U.S. Census records to establish a number of historic dwelling units at a building in Chicago for the purposes of the city generating a “zoning certificate”. That’s a recognition of the number of legal dwelling units especially useful when that number of dwelling units is greater than the current zoning code allows. They’re required to be generated (i.e. requested from the city’s planning department) during the sale of a small-scale residential property.

This Chicago zoning certificate was generated the “normal” way (which I don’t know how to describe), while this blog post is about digging up evidence in case the normal way doesn’t affirm the number of dwelling units you want it to affirm.

However, based on a recent experience of a client of mine, the zoning certificate – while supposedly valid for one year – is subject to dispute later! Finding Census records showing the same or more dwelling units in a given building has helped re-establish the validity of the number of units stated in a zoning certificate.

It will take you some time to research Census records! (I would budget at least one hour. There is a painstaking process to find the webpage that has the enumeration (counting) sheets for the address you want, and it will take some time to sift through those sheets (and you may have to look at multiple pages for the same address).

Here are the steps involved

  1. Find the enumeration district (ED).
  2. Review that ED’s set of sheets in the National Archives 1950 Census website.
  3. Page through and read every sheet until the address is found.

Tip: I recommend doing this, especially step 3, on a computer with the largest screen possible as it’s easier to view the scanned Census sheets that way.

1. Find the enumeration district

The New York Public Library has a great tutorial on their blog, and I recommend you start by reading section #2, “Generate an ED number”.

Once you locate the ED (following the instructions in “Generate an ED number”) I would say stop reading the NYPL blog post.

Alternatively, for Chicago address lookups, you can browse these maps of the enumeration districts and then search for those ED numbers directly on the National Archives website.

2. Review that ED’s set of sheets

The instructions will advise you to use Steve Morse’s third-party Unified Census ED Finder (which is the most useful part of this process). The ED Finder has a wizard asking you to select state, county, city, and street name and cross street. It will then produce a set of one or more ED numbers under the heading, “1950 ED numbers corresponding to your location”.

A screenshot of the ED Finder “wizard”.

Tip: ED Finder will likely show you multiple ED numbers; you may need to look at all of them to find an address. I think this happens because the link between each enumeration district and a city’s streets is imprecise

Click each ED number, which opens a new tab in the ED Finder website with links to three different image viewers. These are databases where scans of microfilm are shown online. One of them, NARA, is public – that’s the National Archives & Records Administration. I recommend that one as it’s free and doesn’t require an account.

3. Read each enumeration sheet

Once you arrive on the NARA website click on the “Population Schedules” to reveal the enumeration sheets. Start paging and reading!

Tip: Street names are written vertically on the left edge of the page.

A screenshot of the 1950 Census database and website of NARA. It’s necessary to click the “population schedules” button to display the enumeration sheets.

The NARA viewer isn’t the best – it doesn’t allow you to make it full-screen; I was constantly having to zoom in to read the street names and house numbers.

A screenshot of a 1950 Census enumeration sheet with two annotations.

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

December 17, 2014 / / 5 Comments

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”.