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You have 2 options for figuring out which Census tracts are in your city. Important Note: What you and me and other normal people would call cities or towns, the Census Bureau calls places.

Option 1. Census Tracts by City for Complex Cities (i.e. New York City, Los Angeles, Chicago)

• • Go to the Census Bureau’s website here: http://www.census.gov/cgi-bin/geo/shapefiles2010/main
  • Download the 2010 Places File for your State & unzip the file.
  • Download the 2010 Census Tract File for the county that your city is in & unzip the file.
  • Open the files in your favorite GIS. My current favorite GIS is the free, light-weight MapWindow.
  • Use the GIS to calculate which Census Tracts intersect your city. I wrote down step-by-step instructions for how to do this via Map Window. You can download these instructions here.

These instructions are a great example of what really happens when you use open source GIS to solve a problem, because I ran into an error when I was using MapWindow. So I included the error & 2 different ways to solve the problem in the instructions.

Also, you can follow the instructions above to figure out block groups by city as well as Census blocks by city.

Option 2. Census Tracts by City for Simple Cities (i.e. Worchestor, MA, Shoshoni, WY)

• Sign up for a 7 day free trial of Cubit.
• In Cubit, type the name of the city into the Find Box to zoom to your city (see the Orange Circle).
• Zoom out slightly until you can see the entire City in the interactive map. The city outline will be a slightly different color than the rest of the map (see the Orange Arrow-the darker shade is the city limits).
• Click on the Polygon tool and draw a polygon slightly inside of the city limits (see the Orange box). Select Tract as the Geography Level if you want Census tract data (see the Purple box). Click Save.

On the next page, you’ll get a labeled map that shows the Census tracts in your city as well as demographic data reports.

Note: if you save your project and Cubit returns a Census tract that you can see is outside of your city, don’t panic. All that means is that some part of your line touched an area that is outside of the city. Click on the Edit Project button. Then, click on the Polygon button. Now, click on the points on your original line to adjust your line inside of the city so that you’ll only get tracts inside of your city. If nothing happens when you click on your original line, try clicking on different points along the line.

Again, you can follow the instructions above to figure out block groups by city as well as Census blocks by city.

The Really Nerdy Background

This blog post came about when I received a request to pull all Census tracts for a city. “No problem,” I thought, “I’ll just go to the Census 2010 data and look up the Places code for Census tracts.”

So I pulled up the Census 2010 data in MySQL and displayed all of the Census Tracts for my state of interest, Massachusetts. Great! There 1478 Census Tracts in Massachusetts. Then, I selected all Census Tracts in Massachusetts where the Place FIPS was not empty. Oh no! That returned 0 rows! That means there are no relationships in the Census 2010 data between Census tracts & Place.

Just to make sure I wasn’t missing something, I double checked the Census 2010 Redistricting PDF Summary Level Sequence Chart, and sure enough, there were no SumLevels with relationships from Cities to Census Tracts (or to BlockGroups or to Blocks for that matter). But don’t take my word for it–click on the link above in this paragraph and go to Summary Level Sequence Chart on page 4-1 to see for yourself.

So you’ll have to use either of the 2 methods above to figure out which Census tracts by City instead using relationships in the raw Census data. Was this post about Census tracts by City helpful or confusing? Any questions here?

If you’re using Mara’s excellent instructions for working with Census 2010 data, you’ll need to know about Summary Levels or SUMLEVs in step 6.

What are Census Summary Levels (SUMLEV)?

Simple Answer: SUMLEV is a Census Bureau code to indicate geography type. For example, in the raw Census 2010 data, all states have a SUMLEV code of “040.”

A Touch of Complexity: SUMLEVs also designate hierarchical relationships for the geographies. For example, a SUMLEV of “050” indicates a County WITHIN a State. A SUMLEV of “140” indicates a Census Tract within a County within a State.

Below is a chart showing SUMLEVs for common geographies.

Geographies	SUMELV	Hierarchy
	Census 2000 & 2010
State	040	State
County	050	State-County
County Subdivison	060	State-County-County Subdivision
Tract	140	State-County-Tract
Block Group	150	State-County-Tract-Block Group
Place(aka City)	160	State-Place

Odd Man Out: Census Blocks

Census Blocks have different Summary levels for Census 2000 and Census 2010.

• For Census 2000, the SUMLEV for Census Blocks is 101. The geographical hierarchy is State-County-County Subdivision-Place/Remainder-Tract-Block Group-Block.
• For the Census 2010, the SUMLEV for Census Blocks are either 750 with a hierarchy of State-County-VotingDistrict/Remainder-County Subdivision-Place/Remainder-Tract-Block Group-Block OR 755 with a hierarchy of State-County-VotingDistrict/Remainder-County Subdivision-Subminor Civil Division-Tract-Block Group-Block.

Below are the original sources for Summary Level data from the Census Bureau. Use these to look up a geography types and SUMLEVs that aren’t listed above.

• Census 2000, Page 4 – 1, http://www.census.gov/prod/cen2000/doc/sf1.pdf
• Census 2010, Page 4 – 1, http://www.census.gov/prod/cen2010/doc/pl94-171.pdf
• American Community Survey ftp://ftp2.census.gov/acs2009_5yr/prod/Geography_Summary_Levels_and_Components.pdf

Photo by Andrew Neel on Unsplash

There is no Census 2010 Long Form.

I still get asked by planners and researchers about when will the Census 2010 Long Form data be released. So I hope to clear up the confusion around this topic. Bottom-line: there is no Census 2010 Long Form. It’s been replaced by the American Community Survey.

Census Short Form versus a Census Long Form

Let’s go back to the Census 2000. The Census 2000 used 2 forms: the Short Form and the Long Form. The Census 2000 Short Form collected basic demographic information from 100% of US residents. The Short Form collected information like population count, sex, age and race. Here’s the Census 2000 Short Form.

The Census 2000 Long Form included all of the Census Short Form questions plus additional, more detailed demographic questions. For example, the Long Form asked about school attendance, languages spoken and disabilities. Here’s the Census 2000 Long Form.

The Census Long Form was sent to only 18 million lucky households–a small sample of the 105.5 million households in the US in 2000. The Census Bureau used the Long Form data collected from the 18 million household sample to then project or estimate the detailed demographic data for the rest of the US households that got the Short Form and weren’t asked the detailed demographic questions.

The Census 2010 Didn’t Use a Long Form

Fastforward to the Census 2010. The decennial Census 2010 only collected basic demographic information (just like the Census 2000 Short Form). The Census Bureau did not include a Long Form Questionnaire in the 2010 Census. Here’s a copy of the 2010 Census Form. You can see that the Census 2010 Form is much more like the Census 2000 Short Form than like the Census 2000 Long Form. In fact, the Census 2010 Form is one of the shortest Census forms in history.

Great, you’re still with me. So since the decennial Census 2010 didn’t use the Long Form, then how are researchers going to get the detailed demographic data like education levels and languages spoken that we need for our planning projects? That’s were the American Community Survey comes in. Just so there’s no confusion, let me quote from the Census Bureau:

Launched in 2005, the American Community Survey (ACS) is part of the decennial census program and is essentially what used to be the long form.

Let me know if you have any other questions about the ACS or Census 2010 in the comments below.

Photo by timothy muza on Unsplash

This post explains the differences between the American Community Survey (ACS) and the Decennial Census and how those differences will impact your work.

Background: Long Form and Short Form

Remember back to the Census 2000 when some people were complaining about the Census form taking forever to fill out? Well, those people received the Census 2000 Long Form which was sent to about 18 million households and collected detailed demographic, economic and housing data. The rest of the US households received the simple Census 2000 Short Form, which was used to count the population and collect basic demographic data. So for the Census 2000, 2 forms were used: the Long Form and the Short Form.

Fast-forward to the Census 2010. The Census 2010 did not use the Long Form, only the Short Form. Enter the ACS. The American Community Survey (ACS) is an annual demographic survey of the United States. It provides the detailed demographic, economic and housing data that was once supplied by the Decennal Census Long Form.

	2000	2010
Count + Basic Data	Short Form	Census 2010
Detailed Data	Long Form	ACS 5 year estimates

However, the ACS is only sent to 3 million households each year, a statistically small sample especially when compared to the Census 2000 Long Form which was sent to 18 million households in 1 year. So to produce the detailed demographic data, the ACS combines data from several years to produce multi-year estimates. For example, the ACS combines data collected from 2006 + 2007 + 2008 to get 3-year ACS estimates for geographies with at least 20,000 persons. ACS 5 year estimates, which will be out in December 2010, will provide data for geographies with fewer than 20,000 persons.

Similar Data; Different Methodologies & Format

The ACS and the Decennial Census provide the same types of data data–that is, demographic, economic and housing data for the US. However, the methodology of these 2 tools differs greatly.

	ACS	Decennial Census
What isIt?	Continuous demographic survey	Count of the population
Data	Average characteristics OVER TIME	Counts characteristics for a SPECIFIC DATE
How Often	Every 1 year (more timely)	Every 10 years (less timely)
House-holds	11 million households over 5 years	18 million households in 1 year
Sampling Error	Higher Error (1.75 percent higher than Census 2000*)	Lower Error
Accuracy	Less Accurate	More Accurate

*[Revised: this information (and much of the blog post) is based on the Census Bureau’s Brian McKenzie’s awesome presentation here]

To sum up the table above, the ACS more timely but less accurate than the Decennial Census, because the data is collected over a series of years (instead of just 1 year), and fewer households are surveyed.

Because the ACS is less accurate, ACS data includes margins or error and is released at 90% confidence limits. Here’s an example of ACS data.

	Austin city
	Estimate	Error	Percent	Error
Hispanic/Latino	261,672	+/-3,404	35.0	+/-0.4

This means that we can say with 90% confidence that the number of Hispanic persons in Austin is between 258,268 and 265,076 (or 261,672 plus or minus 3,404). We can also say with 90% confidence that the percentage of Hispanic persons in Austin is between 34.6% and 35.4%.

How Does All of this Impact You?

1. ACS demographic data is less reliable than Decennial Census data. It’s going to be more important than ever use ACS data as a starting point only and to support the data fieldwork, interviews, and data from other sources.
2. Doing basic calculations with ACS data is going to require an elementary understanding of statistics. For example, calculating percentage change between Census 2000 data and ACS estimates will require basic statistics, because the numbers are not comparable (they are apples to oranges).

If you’re interested, let me know in the comments if a blog post on how to accurately calculate comparisons using Decennial Census data and ACS estimates would be helpful. Or you can check out the Census’ guidance on the topic.  Any questions about the differences between ACS and Decennial Census data? Are there still points of confusion?

Co-written by Aaron Herman

Finding land use land cover data is a pain. Unless your project is within an MPO/COG that has historic and current land use shapefiles that are easy for your GIS guru to access, you can be up a creek without a paddle when it comes to finding good land use data.

Despite the data challenges, many planners HAVE to have land use data for their projects. For example, over 90% percent of transportation environmental impact statements address land use impacts in their indirect impacts analyses according to an unscientific survey. So what should you do if your project is in an area that doesn’t have local land use data? Or what if you have a giant project area and the land use data set for one area doesn’t jive with the land use data set for another area?

USGS Land Use Data

If you can’t find good land use data from the typical local venues (I’ll blog about “typical local venues for land use data” next week), check out the US Geological Survey’s 2001 National Land Cover Data Set (or USGS NLCD 2001). The USGS 2001 National Land Cover Data Set is the latest, most accurate, nearest-to-complete and standardized land use coverage for the entire United States. Yup, you can get land cover data for the whole USA enchilada.

Positives of the USGS 2001 National Land Cover Data Set

• Nationwide land use data for the entire United States
• Standardized land use types makes for easy apples-to-apples comparisons
• Have historic data & are working on more current data set (2006) for visualizing land use trends over time

There is a USGS NLCD 1992 data set. And the land use experts over at the Multi-Resolution Land Characteristics Consortium are working on a USGS NLCD 2006 data set. You can use these USGS National Land Cover Data Sets to visualize land use changes over time.

Negatives of the USGS 2001 National Land Cover Data Set

• 2001 is old
• National land use data won’t be as detailed or current as local land use data
• The data is provided as a image. While it’s possible to convert the image to acreage estimates, it’s technically difficult to do and would involve custom scripting.

Head to Head Battle: Local Data vs. USGS 2001 National Land Cover Data

Let’s compare the land use data provided by Twin Cities’ Metropolitan Council and the USGS NLCD 2001. I was able to download Generalized Land Use 2005 data from the Metropolitan Council for the seven-county area. For comparison, displayed below is the USGS 2001 National Land Cover data for roughly the same area. These images are pretty small–if you need bigger images or want more information about land use land cover data sources, scroll down to the end of the blog post where you can get more information in a pdf.

You can get much more specified data with the local Metropolitan Council data set. For example, I can determine Single Family Attached versus Single Family Detached versus Mobile Homes using the Metropolitan Council’s data. The USGS 2001 National Land Cover data provides generalized data on Developed High Density, Developed Low Density and Developed Medium Density. But not every project area has good, accessible land use data like the Metropolitan Council data. And that’s where USGS 2001 National Land Cover Data comes in handy.

Bottom Line

If you have a small project in an area that has good local land use data, local data is your best bet. If you have a large project area (think multi-county, multi-MPO/COG, especially multi-state) or you can’t find good local data, then check out the USGS 2001 National Land Cover Data Set.

If you need more information about where to get land use land cover data, Aaron Herman researched and wrote an excellent whitepaper on the subject. This blog post is based on his research. If you want a pdf of his whitepaper, contact me here and I’ll send it to you.

Do you have another favorite back-up land use data set that you use? Leave a comment so we can check it out.