GIS for Transportation: Principles, Data and Applications

2.2 Getting to Know a Transportation Organization


This week you’ll take some time to get to know the Census Bureau. 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 surveys and a continuous survey known as the American Community Survey (ACS). The ACS is a continuous survey, similar in structure to the decennial census, which began in 2005 in order to provide more up to date information. Data from both the decennial survey and the ACS are made available in a variety of ways, one of the most popular of which is the American Fact Finder site.

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.

Geographic Areas Used by the Census Bureau

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.

The Census bureau defines many different geometries which can be used to organize and aggregate data. The areas the Census Bureau uses can be divided into those which are legally defined and those which are not. The Census Bureau refers to non-legally defined areas as statistical areas.

Watch the following tutorial (15 minutes) which provides an overview of the geographic areas the Census Bureau uses and the relationships between them.

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 (ASHTO). ASHTO 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. Prior to the ACS, the CTPP consisted of a single data package which was based on the decennial census. Ever since the ACS began in 2005, the CTPP is now comprised of two separate data packages. One is based on 3 years of ACS data, and one is based on 5 years of ACS data. The 5 year data package is used for the examination of smaller geographic regions such as census tracts. In the future, the CTPP package based on 3 year estimates will be replaced with a package based on 1 year estimates. Take a look at the latest CTPP status report to see what they are currently up to.

To facilitate the use of the CTPP data, ASHTO 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. 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 of CTPP Software: Select Geography by List and Map . This will expand to provide more information.

Hi this is Penelope Weinberger. I'm the Census Transportation Planning Products Program Manager at ASHTO. I'm 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 CTPP residents 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 way to access nearly 350 gigs of data provided by the Census Bureau. The dataset consists of almost 200 resident space tables, 115 workplace based tables, and 39 flow tables, 325,000 geographies. The data is derived from the American Community Survey Microdata record based on 2006-2010 ACS. Looking at here is the home screen 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. 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 selected have 52 state selected that includes DC. Like all good GISs I'm going to have to clear my selection I don't want it in the table. So the first I click is clear full selection. Then I have to decide 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 its 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. out says set. If I want save this set of just Maryland counties or any geography 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 for 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 selection. On the map you do that over on right hand side with the little garbage can. Now I pick my level. I want counties again. I want place over counties.

Now I could do this a of number 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 since state 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. 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 flow tables 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 til its 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 Allegheny County. 153,000 live in an 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.

Assignment 2-3 (15 points)

Based on your review of Census geographies and the CTPP, submit a write-up in M.S. Word format to Assignment 2-3 in Canvas which addresses the following 6 items:

  1. Based on your review of Census geographies, list 3 legal geographic areas the Census Bureau uses as well as 3 statistical areas they use. (2 points)
  2. Which is the smallest geographic area the Census Bureau uses? (1 point)
  3. Use the CTPP data analysis tool and the 2006 – 2010 ACS data to answer the following questions (hint: follow a procedure similar to that used in the YouTube video referenced in the lesson):
    1. Which three counties in Pennsylvania have the highest number of workers who commute to Centre County for work (other than Centre County itself)? (2 points)
    2. Which three counties in Pennsylvania have the highest number of workers who live in Centre County (other than Centre County itself)? (2 points)
    3. View the results of the above analysis as a thematic map. Generate a thematic map showing workers who flow into Centre County for work and who flow out of Centre County for work. Grab a screen shot of each and include it in your submittal. (2 points)
  4. Do the results of Mark Evans' tool qualitatively agree with the CTPP data analysis tool? (2 points)
  5. Referring to the latest CTPP status report, what is the mission of the CTPP? (2 points)
  6. In regard to the CTPP, why do you think the 5 year ACS estimates are needed for smaller geographies? (2 points)