GIS for Transportation: Principles, Data and Applications

2.3 Getting to Know a Transportation Organization


In preparation for this week's webinar, you learned about the geographic areas the Census Bureau uses to tabulate and disseminate data. This week, you’ll explore the Census Bureau in greater detail. The Census Bureau is part of the U.S. Department of Commerce. The mission of the Census Bureau is to “serve as the leading source of quality data about the nation's people and economy.” To fulfill its data gathering objectives, the Bureau conducts both decennial censuses and a continuous survey known as the American Community Survey (ACS). The ACS was born in 2005 out of a need for more up-to-date information than the decennial census provided. Data from both the decennial census and the ACS are made available in a variety of ways, one of the most popular of which is the via the American FactFinder site.

Take a look through the American Community Survey Information Guide which the Census Bureau updated in December 2017.

Data collected by the Census Bureau serve some critical functions. These data are used to:

  • determine the number of seats each state has in the house of representatives;
  • distribute over 400 billion dollars in federal funding annually;
  • make planning decisions about community services.

Geography and GIS are very important to the Census Bureau.

Watch this brief presentation on the Maps of the US Census Bureau (5 minutes) by Atri Kalluri, Assistant Division Chief of the US Census Bureau.

Census data have long been applied to transportation planning and research. Today, there are a number of emerging sources of data which serve to compete with or complement the role of the census data in these fields. Read this 2017 paper by Gregory D. Erhardt (University of Kentucky) and Adam Dennett (Centre for Advanced Spatial Analysis, University College, London) which examines this topic.

Census Transportation Planning Products Program

The Census Transportation Planning Products Program (CTPP) is an initiative led by the American Association of State Highway and Transportation Officials (AASHTO). AASHTO is an organization we’ll take a closer look at in an upcoming lesson. The CTPP provides special tabulations of Census data which are of particular interest to transportation planners. These datasets provide insight into how people commute and which modes of transportation they use. They are often used to validate travel demand models which themselves are used to make decisions on what types of transportation projects are needed to support regional needs, including those related to economic growth, public health, transit needs, and highway safety issues (for a quick overview of the Four Step Model (FSM) which commonly used in travel demand modeling, see this 2007 article by Michael McNally at the University of California, Irvine).

To facilitate the use of the CTPP data, AASHTO created a web-based application to examine travel flows. The CTPP even has a YouTube channel devoted to teaching people how to use the software (although the quality of the videos is less than stellar). Take a look at the YouTube video below (5 minutes) which shows how to generate some basic county to county commuter flow data. The CTPP data analysis tool also has the ability to display results in a variety of formats including thematic maps.

Click for transcript.

Hi, this is Penelope Weinberger. I'm the Census Transportation Planning Products Program Manager at ASHTO, recording some brief tutorials on the CTPP data access software. The tutorial you're about to watch is on selecting geography. There are two parts to the CTPP, residence and workplace, and there are two ways to select geography, by list and by map. We're going to look at both of those.

The CTPP data access software is a powerful tool to access the nearly 350 gigs of data provided by the Census Bureau. The dataset consists of almost 200 residence-based tables, 115 workplace-based tables, and 39 flow tables from (inaudible), 325,000 geographies. The data is derived from the American Community Survey Microdata record based on the 2006-2010 ACS. Looking at here is the home screen for the CTPP data access software. I'm not going to select a table. I'm going to go straight to selecting geography. As you can see, I have Residence geography by the red box and Workplace geography by the blue box. The default geography for all CTPP tables is States. We're going to change that right now. I'm going to click on Residence, and the software is going to open up and show me. On the left-hand side of the screen, I'm looking at my select level. State is what's highlighted, and States are what are selected. I have 52 states selected, that includes DC and Puerto Rico. Like all good GISs, I'm going to have to clear my selection if I don't want it in the table. So, the first thing I do is hit clear full selection. Then, I have to decide what level of geography I'm interested in. I'm interested in counties. There are 3,221 counties in the US, and I have none of them selected. So, first, I pick my level, and then it's gonna give me a list starting in Alabama. Well, I don't want to scroll all the way down from Alabama to Maryland, so I'm gonna search for Maryland, instead. I put my cursor in the search box, and I type Maryland, and then click on the search tool and also hit enter.

In the CTPP, you can have mixed levels of geography. This tutorial is just going to look at counties. Now, I have my 24 counties in Maryland. I'm gonna choose to select all of them, and I click the Select All button on the right-hand side, check marks by each one. Pretty Nifty! Now, I want to pick my workplace geography. I'm actually gonna pick the same geography. I do want you to take note that where it said all states before, now it says new set. If I want to save this set of just Maryland counties or any geography I create, we'll have to sign in, but I'm not going to do that today. Now, I'm just gonna click on workplace, and instead of picking by list, I'm gonna pick by map. So, instead of using the selection list tab, I'm going to use the selection map tab. Click on that, and it shows me a cool map of the United States. Of course, I have all my states selected since that's my default. So, I'm going to clear the selection. On the map, you do that over on the right-hand side with the little garbage can. (...they go!) Now, I pick my level. I want counties again. I want place over counties.

Now, I could do this a number of ways. I could zoom in with my tool just to where I happen to know Maryland is, and I could pick the counties one by one. That could be a little bit tedious. So, instead, I'm going to use this cool Zoom To and Select tool. Place over state is what I want cause that is the parent. Down here, it says automatically highlight any place over County. I click that on, I type in Maryland. Hit Enter. It's loading up my Maryland counties. Now look, 24 place over counties. It's good those two numbers match. Do I want to add all highlighted counties to my selection? I do. So, I click that, and there they all are.

Now, let's see if I can look at a table with my county residences and my county workplaces. Show CTPP tables. Of course, I want a flow table since I've got two geographies selected. Workers, let's just look at total workers. Now, one thing that's a little odd about this table, is that the residence and the workplace are both on the [INAUDIBLE], so I'm going to move one of those so that I have a matrix. I like my data as is. I'm going to grab my Residence by the textured box to the left of the word, and I'm going to drag it up till it is over output with that up-pointing arrow. I'm going to drop it. Now my output is going to nest on the Residences. It's a great-looking matrix. I have 25,000 workers that live in Allegheny and that work in Allegheny County. 153,000 live in Anne Arundel and work in Anne Arundel. It should go right down that way, the biggest numbers now in the matrix. Sure looks like it does.

Another interesting use of the commuter flow data can be seen in an application created by Mark Evans. Mark used the Google Maps API to create a GIS application called Commuter Flows which facilitates the visualization of census tract level commuter flows derived from the ACS data.