Posts Tagged ‘census’

Review of The Census Reporter

Monday, February 8th, 2016

Picking up where I left off from my previous post (gee – welcome to 2016!) I thought I’d give a brief review of another census resource, The Census Reporter at http://censusreporter.org/.

The Census Reporter was created to make it easier for journalists to write stories using census data. To that end, they’ve created a really slick and easy to use web site that makes the data accessible and fun to explore. From the homepage you have three ways of diving into the data: you can pull up a profile by typing in the name of a place, you can enter an address and explore places that contain that address, or you can explore tables by topic.

Census Reporter Homepage

First, the place-based approach. You can type in a named place, like a state, county, or a census place (incorporated cities and towns, or census designated places) to get started. This will give you a selection of data from the most recent release of the American Community Survey. For larger areas where the data is available, it gives you 1-year ACS data by default; otherwise you get the latest 5-year data.

You’re presented with a map of the location at the top, and a series of attractive looking graphs and charts sorted by the demographic profile table source – social, economic, housing, and demographic. If you hover over a data point in a table it gives you some geographic context by comparing this place’s value with that of larger places where it’s contained. For example, if I search for Philadelphia I can hover over the chart to get the value for the Philly metro area and the State of Pennsylvania. I can click a link below each chart to open the full table, which includes both estimates and margins of error. There are small links for viewing the table by itself on a separate page (which also gives you the ability to download it) and for embedding the chart in a website.

Census Reporter Chart and Table

Viewing the table gives you additional options, like adding additional places for comparison, or subdividing the place into smaller areas for comparison. So if I’m looking at Philadelphia, I can break it down into tracts, block groups, or ZIP Codes. From there I can toggle away from the table view to view a map or a distribution bar to explore that variable by individual geographies.

View Data by Sub-Areas, Distribution Bars

The place-based search is great at allowing you to drill down either by topic or by these smaller geographies. But if you wanted to access a fuller range of geographies like congressional districts or PUMAs, it seems easier to do an address-based search. Back on the homepage, selecting the address button and typing in an address brings you to a map with the address pin-pointed, and on the left you can choose any geography that encloses that address. Once you do that, you get a profile for that geography and can start doing the same sorts of operations for changing the topics or tables, or adding or subdividing geographies for comparison.

Address Search

The topic-based search lets you search just by topic and then figure out the geography piece later. Of the three types of searches this one is the toughest, given the sheer number of tables and cross-tabulations. You can click on a link for a general topic to narrow things down a bit before beginning a search.

In downloading the data you have a variety of useful options: CSV, Excel, GeoJSON, KML, and shapefiles. So in theory you can download data that’s readily mappable – in practice I wasn’t able to download a shapefile, but could grab a KML or GeoJson and was able to visualize it in QGIS. One challenge in downloading any of the files is that the column names use the identifier codes, and the actual names of the variables aren’t included in the download format you choose – they’re included in a json file. So you can use that for reference, but it can’t be readily incorporated into the table.

So – where would this resource fall within the pantheon of US Census data resources? I think it’s great for accessing and, especially, visualizing profiles (profile = lots of data for one place) from the most recent ACS releases. It’s easy to use and succeeds at making the data interesting; for that reason I certainly would incorporate it into undergraduate courses where I’m introducing data. The ability to embed the charts into websites is certainly a bonus, and they deserve a big thumbs up for incorporating the margin of error data, rather than hiding or discarding it like other resources do.

The ability to create and view comparison tables (comparison = one piece of data for many places) is good – select an area and then break it down – but not as strong as the profile options. If you want to get a profile for a non-named place like a tract, ZIP Code, or PUMA you can’t do that from the profile search. You can do an address search and back out (if you know an address for that you’re interested in) or you can drill down by topic, which lets you search by summary area in addition to named places.

For users who need to download a lot of data, or for folks who need datasets that aren’t the most recent ACS release, this resource isn’t the place to go. The focus here is on providing the data in an easy and compelling way, as is. In viewing the profiles, it’s not clear if you can choose 5-year data over 1-year data for places where both datasets are available – even for large geographic areas with high population, sometimes it’s preferable to use the 5-year data to take advantage of the smaller margins of error. I also didn’t see an option for choosing decennial census data.

In short, this resource is well-designed and definitely worth exploring. It seems clear why this would be a go-to source for journalists, but it can be for many others as well.

The New NYC Census Factfinder

Wednesday, September 9th, 2015

As I’m updating my presentations and handouts for the new academic year, I’m taking two new census resources for a test drive. I’ll talk about the first resource in this post.

The NYC Department of City Planning has been collating census data and publishing it for the City for quite some time. They’ve created neighborhood tabulation areas (NTAs) by aggregating census tracts, so that they could publish more reliable ACS data for small areas (since the margins of error for census tracts can be quite large) and so that New Yorkers have data for neighborhood-like areas that they would recognize. The City also publishes PUMA-level data that’s associated with the City’s Community Districts, as well as borough and city-level data. All of this information is available in a large series of Excel spreadsheets or PDFs in the form of comparison tables for each dataset.

The Department of Planning also created the NYC Census Factfinder, a web-mapping interface that let’s users explore census tract and NTA level data profiles. You could plug in an address or click on the map and get a 2010 Census profile, or a demographic change profile that showed shifts between the 2000 and 2010 Census.

pic1_factfinder

It was a nice application, but they’ve just made a series of updates that make it infinitely better:

  1. They’ve added the American Community Survey data from 2009-2013, and you can view the four demographic profile tables (demographics, social, economic, and housing) for tracts and NTAs.
  2. Unlike many other sources, they do publish the margin of error for all of the ACS data, which is immensely important. Estimates that have a high margin of error (as defined by a coefficient of variation) appear in grey instead of solid black. While the actual margins are not shown by default, you can simply click the Show radio button to turn on the Reliability data.
  3. Tracts or neighborhoods can be compared to the City as a whole or to an individual borough by selecting the drop down for the column header.
  4. This is especially cool – if you’re viewing census tracts you can use the select pointer and hold down the Control key (Command key on a Mac) to select multiple tracts, and then the data tables will aggregate the tract-level data for you (so essentially you can build your own neighborhoods). What’s noteworthy here is that it also calculates the new margins of error for all of the derived estimates, AND it even calculates new medians and averages with margins of error! This is something that I’ve never seen in any other application.
  5. In addition to searching for locations by address, you can hit the search type drop down and you have a number of additional options like Intersection, Place of Interest, and even Subway Stations.

nyc_factfinder_table

There are a few quirks:

  1. I had trouble viewing the map in Firefox – this isn’t a consistent problem but something I noticed today when I went exploring. Hopefully something temporary that will be corrected. Had no problems in IE.
  2. If you want to click to select an area on the map, you have to hit the select button first (the arrow beside the zoom slider and print button) and then click on your area to select it. Just clicking on the map without hitting select first won’t do much – it will just highlight the area and tell you it’s name. Clicking the arrow button turns it blue and allows you to select features, clicking it again turns it white and lets you identify features and pan around the map.
  3. factfinder_buttons

  4. The one bummer is that there isn’t a way to download any of the profiles – particularly the ones you custom design by selecting tracts. Hitting the Get Data button takes you out of the Factfinder and back to the page with all of the pre-compiled comparison tables. You can print the table out to a PDF for presentation purposes, but if you want a data-friendly format you’ll have to highlight and select the table on the page, copy, and paste into a spreadsheet.

These are just small quibbles that I’m sure will eventually be addressed. As is stands, with the addition of the ACS and the new features they’ve added, I’ll definitely be integrating the NYC Census Factfinder into my presentations and will be revising my NYC Neighborhood Census data handout to add it as a source. It’s unique among resources in that it provides NTA-level data in addition to tract data, has 2000 and 2010 historical change and the latest 5-year ACS (with margins of error) in one application, and allows you to build your own neighborhoods to aggregate tract data WITH new margins of error for all derived estimates. It’s well-suited for users who want basic Census demographic profiles for neighborhood-like areas in NYC.

Census Proposes to Cut 3-year ACS in Fiscal 2016

Friday, February 6th, 2015

I’m coming out of my blog hibernation for this announcement – the US Census Bureau is proposing that they drop the 3-year series of the American Community Survey in fiscal year 2016. A colleague mentioned that he overheard this at a meeting yesterday. Searching the web, I found a post at the Free Government Information site which points to this Census Bureau Press release. The press release cites the predictable reasons (budget constraints, funding priorities, etc.) for dropping the series. Oddly, the news comes through some random site and not through the Census Bureau’s website, where there’s no mention of it. I saw that Stanford also had a post, where they shared the same press release.

I kept searching for some definitive proof, and through someone’s tweet I found a link to a PDF of the US Census Bureau’s Budget Estimates for Fiscal Year 2016, presented to Congress this February 2015. I found confirmation buried on page CEN – 106 (the 100th page in a 190 page doc):

Data Products

Restoration of ACS Data Products ($1.5 million): Each year, the ACS releases a wide range of data products widely used by policymakers, Federal, state and local governments, businesses and the public to make decisions on allocation of taxpayer-funds, the location of businesses and the placement of products, emergency management plans, and a host of other matters. Resource constraints have led to the cancellation of data products for areas with populations between 20 and 60 thousand based on 3-year rolling averages of ACS data (known as the “3-Year Data” Product).They have also resulted in delays in the release of the 1- and 5- year Public Use Macro Sample (PUMS) data files and canceled the release of the 5- year Comparison Profile data product and the Spanish Translation of the 1- and 5- year Puerto Rico data products.

The Census Bureau proposes to terminate permanently the 3-Year Data Product. The Census Bureau intended to produce this data product for a few years when the ACS was a new survey. Now that the ACS has collected data for nearly a decade, this product can be discontinued without serious impacts on the availability of the estimates for these communities.

The ACS would like to restore the timely release of the other essential products in FY2016. The continued absence of these data products will impact the availability of data – especially for Puerto Rico – to public and private sector decision makers.

So at this point it’s still just a proposal. The benefits, besides the ability to release other datasets in a timely fashion, would be simplification for users. Instead of choosing between three datasets now there will only be two – the one year and the five year. You choose the one year for large areas and the five year for every place else. In terms of disadvantages, consider this example – here are the number of children enrolled in nursery school in NY State PUMA 03808, which covers Murray Hill, Gramercy, and Stuyvesant Town in the eastern half of Midtown Manhattan:

PUMA NY 03808

Population Over 3 Years Old Enrolled in Nursery / Pre-school

  • 1 year 2013: 1,166 +/- 609
  • 3 year 2011-2013: 1,549 +/- 530
  • 5 year 2009-2013: 1,819 +/- 409

Since PUMAs are statistical areas built to contain 100k people, data for all of them is available in each series. Like all the ACS estimates these have a 90% confidence interval. Look at the data for the 1-year series. The margin of error (ME) is so large that’s it’s approximately 50% of the estimate, which in my opinion makes it worthless for just about any application. The estimate itself is much lower than the estimate for the other two series. It’s true that it’s only capturing the latest year, but administrative data and news reports suggest that the number of nursery school children in the district that covers this area has been relatively stable over time, with modest increases (geographically the district covers an area much larger than this PUMA). This suggests that the estimate itself is not so great.

The 5 year estimate may be closer to reality, and its ME is only 20% of the estimate. But it covers five years in time. If you wanted something that was a compromise – more timely than the five year but with a lower ME than the one year, then the three year series was your choice, in this case with an ME that’s about 33% of the estimate. But under this proposal, this choice goes away and you have to make do with either 1-year estimates (which will be lousy for geographies that aren’t far above the 65k population threshold, and lousy for small population groups where ever they are located), or better 5-year estimates that cover a greater time span.

Government Shutdown: Alternate Resources for US Census Data

Sunday, October 13th, 2013

As the US government shutdown continues (thanks to a handful of ideological nutcases in congress) those of us who work with and rely on government data are re-learning the lesson of why it’s important to keep copies of things. This includes having alternate sources of information floating around on the web and in the cloud, as well as the tried and true approach of downloading and saving datasets locally. There have been a number of good posts (like this succinct one) to point users to alternatives to the federal sources that many of us rely on. I’ll go into more detail here with my suggestions on where to access US Census data, based on user-level and need.

  • The Social Explorer: this web-mapping resource for depicting and accessing US Census data from 1790 to present (including the 2010 Census and the latest American Community Survey data) is intuitive and user-friendly. Many academic and public libraries subscribe to the premium edition that provides full access to all features and datasets (so check with yours to see if you have access), while a basic free version is available online. Given the current circumstances the Social Explorer team has announced that it will open the hatch and provide free access to users who request it.
  • The NHGIS (National Historic GIS): this project is managed by the Minnesota Population Center and also provides access to all US Census data from 1790 to present. While it’s a little more complex than the Social Exlorer, the NHGIS is the better option for downloading lots of data en-masse, and is the go-to place if you need access to all datasets in their entirety, including all the detail from the American Community Survey (as the Social Explorer does not include margins of error for any of the ACS estimates) or if you need access to other datasets like the County Business Patterns. Lastly – it is the alternative to the TIGER site for GIS users who need shapefiles of census geography. You have to register to use NHGIS, but it’s free. For users who need microdata (decennial census, ACS, Current Population Survey), you can visit a related MPC project to the NHGIS: IPUMS.
  • The Missouri Census Data Center (MCDC): I’ve mentioned a number of their tools in the past; they provide easy-to-access profiles from the 2010 Census and American Community Survey, as well as historical trend reports for the ACS. For intermediate users they provide extract applications for the 2010 Census and ACS for creating spreadsheets and SAS files for download, and for advanced users the Dexter tool for downloading data en-masse from 1980 to present. Unlike the other resources no registration or sign-up is required. I also recommend the MCDC’s ACS and 2010 Census profiles to web designers and web mappers; if you’ve created online resources that tapped directly into the American Factfinder via deep links (like I did), you can use the MCDC’s profiles as an alternative. The links to their profiles are persistent and use a logical syntax (as it looks like there’s no end in site to this shutdown I may make the change-over this week). Lastly, the MCDC is a great resource for technical documentation about geography and datasets.
  • State and local government: thankfully many state and local governments have taken subsets of census data of interest to people in their areas and have recompiled and republished it on the web. These past few weeks I’ve been constantly sending students to the NYC Department of City Planning’s population resources. Take a look at your state data center’s resources, as well as local county or city planning departments, transportation agencies, or economic development offices to see what they provide.

Article on Working With the American Community Survey

Monday, June 17th, 2013

I’ve got another article that’s just hit the presses. In this one I discuss the American Community Survey: how it differs from the Decennial Census, when you should use it versus other summary data sets, how to work with the different period estimates, and how to create derived estimates and calculate their margins of error. For that last piece I’ve essentially done an extended version of this old post on Excel formulas, with several different and updated examples.

The article is available via Emerald’s journal database. If you don’t have access to it from your library feel free to contact me and I’ll send you a copy (can’t share this one freely online).

Title: The American Community Survey: practical considerations for researchers
Author(s): Francis P. Donnelly
Citation: Francis P. Donnelly, (2013) “The American Community Survey: practical considerations for researchers”, Reference Services Review, Vol. 41 Iss: 2, pp.280 – 297
Keywords: American Community Survey, Census, Census geography, Data handling, Decennial census, Demographic data, Government data processing, Government information, Margins of error, Sample-based data, United States of America, US Census Bureau
Article type: Technical paper
DOI: 10.1108/00907321311326228 (Permanent URL)
Publisher: Emerald Group Publishing Limited

NYC Geodatabase in Spatialite

Wednesday, February 6th, 2013

I spent much of the fall semester and winter interim compiling and creating the NYC geodatabase (nyc_gdb), a desktop geodatabase resource for doing basic mapping and analysis at a neighborhood level – PUMAs, ZIP Codes / ZCTAs, and census tracts. There were several motivations for doing this. First and foremost, as someone who is constantly introducing new people to GIS it’s a pain sending people to a half dozen different websites to download shapefiles and process basic features and data before actually doing a project. By creating this resource I hoped to lower the hurdles a bit for newcomers; eventually they still need to learn about the original sources and data processing, but this gives them a chance to experiment and see the possibilities of GIS before getting into nitty gritty details.

Second, for people who are already familiar with GIS and who have various projects to work on (like me) this saves a lot of duplicated effort, as the db provides a foundation to build on and saves the trouble of starting from scratch each time.

Third, it gave me something new to learn and will allow me to build a second part to my open source GIS workshops. I finally sat down and hammered away with Spatialite (went through the Spatialite Cookbook from start to finish) and learned spatial SQL, so I could offer a resource that’s open source and will compliment my QGIS workshop. I was familiar with the Access personal geodatabases in ArcGIS, but for the most part these serve as simple containers. With the ability to run all the spatial SQL operations, Spatialite expands QGIS functionality, which was something I was really looking for.

My original hope was to create a server-based PostGIS database, but at this point I’m not set up to do that on my campus. I figured Spatialite was a good alternative – the basic operations and spatial SQL commands are relatively the same, and I figured I could eventually scale up to PostGIS when the time comes.

I also created an identical, MS Access version of the database for ArcGIS users. Once I got my features in Spatialite I exported them all out as shapefiles and imported them all via ArcCatalog – not too arduous as I don’t have a ton of features. I used the SQLite ODBC driver to import all of my data tables from SQLite into Access – that went flawlessly and was a real time saver; it just took a little bit of time to figure out how to set up (but this blog post helped).

The databases are focused on NYC features and resources, since that’s what my user base is primarily interested in. I purposefully used the Census TIGER files as the base, so that if people wanted to expand the features to the broader region they easily could. I spent a good deal of time creating generalized layers, so that users would have the primary water / coastline and large parks and wildlife areas as reference features for thematic maps, without having every single pond and patch of grass to clutter things up. I took several features (schools, subway stations, etc) from the City and the MTA that were stored in tables and converted them to point features so they’re readily useable.

Given that focus, it’s primarily of interest to NYC folks, but I figured it may be useful for others who wish to experiment with Spatialite. I assumed that most people who would be interested in the database would not be familiar with this format, so I wrote a tutorial that covers the database and it’s features, how to add and map data in QGIS, how to work with the data and do SQL / spatial SQL in the Spatialite GUI, and how to map data in ArcGIS using the Access Geodb. It’s Creative Commons, Attribution, Non-Commercial, Share-alike, so feel free to give it a try.

I spent a good amount of time building a process rather than just a product, so I’ll be able to update the db twice a year, as city features (schools, libraries, hospitals, transit) change and new census data (American Community Survey, ZIP Business Patterns) is released. Many of the Census features, as well as the 2010 Census data, will be static until 2020.

ACS Trend Reports and Census Geography Guide

Sunday, February 12th, 2012

I recently received my first question from someone who wanted to compare 2005-2007 ACS data with 2008-2010. With the release of the latter, we can make historical comparisons with the three year data for the first time since we have estimates that don’t overlap. We should be able to make some interesting comparisons, since the first set covers the real estate boom years (remember those?) and the second covers the Great Recession. One resource that makes such comparisons relatively painless is over at the Missouri Census Data Center. They’ve put together a really clean and simple interface called the ACS Trends Menu, which allows you to select either two one period estimates or two three period estimates and compare them for several different census geographies – states, counties, MCDs, places, metros, Congressional Districts, PUMAs, and a few others – for the entire US (not just Missouri). The end result is a profile that groups data into the Economic, Demographic, Social, and Housing categories that the Census uses for its Demographic Profile tables. The calculations for change and percent change for the estimates and margins of error are done for you.

Downloading the data is not as straightforward – the links to extract it just brought me some error messages, so it’s still a work in progress. Until then, a simple copy and paste into your spreadsheet of choice will work fine.

ACS Trends Menu

If you like the interface, they’ve created separate ones for downloading profiles from any of the ACS periods or from the 2010 Census. The difference here is that you’re looking at one time frame; not across time periods. The interface and the output are the same, but in these menus you can compare four different geographies at once in one profile. Unlike the Trends reports, both the ACS and 2010 Census profiles have easy, clear cut ways to download the profiles as a PDF or a spreadsheet. If you’re happy with data in a profile format and want an interface that’s a little less confusing to navigate than the American Factfinder, these are all great alternatives (and if you’re building web applications these profiles are MUCH easier to work with – you can easily build permanent links or generate them on the fly).

The US Census Bureau also recently put together a great resource called the Guide to State and Local Census Geography. They provide a census geography overview of each state: 2010 population, land area, bordering states, year of entry into the union, population centroids, and a description of how local government is organized in the state – (i.e. do they have municipal civil divisions or only incorporated cities and unincorporated land, etc). You get counts for every type of geography – how many counties, tracts, ZCTAs, and so on, AND best of all you can download all of this data directly in tab delimited files. Need a list of every county subdivision in a state, with codes, land area, and coordinates? No problem – it’s all there.

2010 Census Generalized Cartographic Boundary Files

Thursday, December 22nd, 2011

I’ve had a few interesting projects that have kept me busy at the end of this year. I’ll do a post or two after New Years, once I’m back in the office and can take some screen shots to illustrate.

In the meantime I have one tidbit I can mention – the Census Bureau has released the 2010 version of the Generalized Cartographic Boundary Files. These files are generalized versions of the TIGER files, with smoothed and simplified boundaries and areas of coastal water removed. They haven’t posted them on the same page as the 2000 and 1990 boundaries; they’ve mentioned they’re creating a new interface to host all of them, which is currently a work in process at http://www.census.gov/geo/www/cob/.

However, you can get access to all the 2010 boundaries via the FTP site – you just need to know what you’re looking at. All the files are named with codes to identify the geographic coverage, summary level, and resolution / scale. There’s a README file on the FTP page that tells you how to identify each.

But in brief – The file names look like this: gz_2010_ss_lll_vv_rr.zip, where:

  • ss is the state INCITS / FIPS code which you can look up here – ‘us’ is a national level file.
  • lll is the summary level or unit of geography – the README file has a table with each code. The most common ones: 040 for state, 050 for county, 060 for county subdivisions, 140 for census tracts, 160 for places, 310 for metropolitan and micropolitan statistical areas, 860 for ZCTAs. (No PUMAs- 2010 PUMA boundaries haven’t been drawn yet, and 2000 PUMA boundaries are still being used in the latest ACS).
  • vv is a version number for the file.
  • rr is resolution – most of the files are 500k = 1:500,000, which is the least generalized and best for mapping state-level to regional areas. For national level files you also have the option of 5m = 1:5,000,000 and 20m = 1:20,000,000, which are more generalized and better for national mapping.

The Census Bureau has been doing a lot of tweaking to their website lately. The legacy version of the American Factfinder is set to disappear for good on Jan 20, 2012.

2010 American Community Survey Releases

Friday, September 23rd, 2011

The US Census Bureau released the new annual data for the 2010 American Community Survey; this dataset includes an extensive number of demographic, socio-economic, and housing estimates (with margins of error) for all geographic areas in the US that have a population of at least 65,000 people. This is the first ACS survey that is weighted based on the 2010 Census, and that is tabulated entirely on the new 2010 Census geography; exceptions include PUMAs and urban areas, which typically aren’t redrawn until a couple of years after a decennial census is taken. Data for these areas will be reported based on the 2000 Census geography. This will also be the first ACS that is distributed via the new American Factfinder. Previous ACS datasets should be moved to the new Factfinder by the end of this year.

According to the release schedule data for the three year ACS (2008-2010) for areas with at least 20,000 residents will be published in October and the five year ACS (2006-2010) for geography down to census tracts will be released in December. The three year dataset hits a milestone this year, as for the first time we’ll have datasets with mutually exclusive years that can be feasibly compared for historical change (the 2005-2007 dataset versus 2008-2010). It should prove interesting as the earlier dataset represents the end of the brief boom years while the current one depicts the depth of the great recession. There will be some challenges in making comparisons, as the base for weighting the estimates and the geography used to tabulate them is different for each dataset (2000 Census in the earlier dataset versus 2010 Census in the latest one).

Relating ZIP Codes / ZCTAs to PUMAs

Saturday, March 19th, 2011

Ever since I created the Google Maps finding aid for census data for NYC PUMAs and the associated PUMA – NYC neighborhood names maps, I’ve received several requests for tables or maps that relate PUMAs to ZIP Codes. These are usually from non-profits in NYC who have lists of donors, members, or constituents with addresses, and they want to relate the addresses (using the ZIP) to recent demographic data from American Community Survey (ACS) for the broader neighborhood where the ZIP is located.

The problem is that ZIP Codes are an all around pain. They actually don’t exist as areas with distinct boundaries; ZIP Codes are all address based, with ZIPs tied to addresses along street segments. The USPS doesn’t publish these tables or create maps; they contract this out for private companies to do, who turn around and sell these products for hefty fees.

Fortunately the Census Bureau has used these address tables to create approximations of ZIP Codes that they call ZCTAs or ZIP Code Tabulation Areas. ZCTAs are aggregates of census blocks that attempt to mimic ZIP Codes that exist as areas; codes associated with specific single-point firms or organization are dropped. Since ZIPS were created by the USPS, ZCTAs do not nest or mesh with any census geography; they cross PUMA, county, and in some cases even state boundaries. They are also less stable than census geography, with frequent changes, and as statistical areas they vary widely in area and population. For this reason ZCTA data is only published every ten years in the decennial census; it’s not included in the ACS (so far).

With these caveats in mind, I used the Missouri Census Data Center’s MABLE/GEOCORR engine to correlate ZCTAs with PUMAs. While the interface looks a little retro and daunting, it’s actually pretty simple. You choose the state, the two geographies you want to relate, the weighting method for allocating one to the other, and an output format that includes CSV or HTML. I also used an option that lets you type in FIPS codes for the counties you want, so I didn’t end up with the entire state.

This method was the way to go, as they give you the option to allocate geographies based on population and not simply land area; each ZCTA was allocated to PUMAs based on where the majority of the ZCTA’s population lived using 2000 census block data. The final output contains one row for each ZCTA to PUMA combination. So you had multiple rows for ZCTAs that weren’t contained within a single PUMA, and for each of those ZCTAs you had fields that showed the percentage of the ZCTA’s population that lived in each PUMA (along with the actual population number) as well as the percentage of the PUMA’s population that lived in that ZCTA.

I took that table and cleaned it up in a spreadsheet, so that I was left with one row for each ZCTA, where the ZCTA was allocated to one PUMA based on where the majority of it’s population lives. I used some ZCTA and PUMA boundaries that I had originally downloaded and subsequently cleaned up from the 2009 TIGER shapefiles page, added them to QGIS, joined the ZCTA allocation table to the ZCTA geography, and mapped the result. I color-coded ZCTAs so that clusters of ZCTAs within a particular PUMA had the same color. Then I overlaid the PUMA boundaries on top to see how well they corresponded.

In the end, they didn’t correspond all that well. There was a fairly good relationship in Manhattan, ok relationship in Queens and Staten Island, and a rather lousy relationship in the Bronx and Brooklyn. I overlaid greenspace and facilities (airports, shipyards, etc) boundaries I had, and that made some difference; you could see in some areas where ZCTAs overlapped two PUMAs that the overlap coincided with parks, cemeteries, or other areas with low or no residential population in one of the PUMAs.

I’ve posted both sets of tables, maps, and some instructions on the NYC neighborhoods resource page. You can use the original MABLE / GEOCORR table to judge where allocations were good and were they were not so good based on population. For now, the engine is still based on 2000 Census geography and data. Even though the Census has started releasing 2010 TIGER files based on 2010 Census geography, ZCTAs and PUMAs are often some of the last geographies to be updated; current releases of the ACS are still based on the 2000 geographies. Stay tuned to the Census Bureau and MCDC websites for news on updates, and keep the MABLE / GEOCORR in mind if you want to create lists to relate census geographies by population or land area.


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