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Drawing the Boundaries of Suburban Geography

Suburbs can be amorphous and hard to grasp. Where does a city end and a suburb begin? Where does a suburb end and a rural area start? Reportedly, 52% of Americans describe their home neighborhood as suburban. Yet, the US Census does not have a definition for a suburban area. The term suburban is considered more of a colloquialism in today’s world. 

In this piece we will look at how MSG defines suburban geography and how the geo-demographic team compensates for the US Census’ shortcomings and discrepancies.

To define a suburban area properly, we must look at all underlying geographic components – in particular urban and rural. To do this, we start by looking at Metropolitan Statistical Areas (MSA) as defined by the Office of Management and Budget (OMB). 

MSA’s are defined as urban areas of at least 50,000 people with one or more adjacent counties that are socioeconomically tied to that urban center. There are over 360 MSA’s currently defined in the US and each MSA has one or more principal cities. 

Traditionally, we consider principal cities to be the core socioeconomic center with the counties surrounding it dependent on it.  

Now, let’s think about how the US Census delineates cities and urbanity. The Census defines urban as being within the principal city of an MSA and any census block outside of the principal city that meets a specific population threshold. 

The problem is that the US Census does not distinguish between suburban or rural areas. It just assumes that anything not urban is rural. In fact, no government entity defines what a suburban area is.

Here we encounter a massive disconnect. According to Pew Research, a growing share of the population in the United States is living in suburban counties of large metropolitan areas. And as we already noted, a majority of Americans say they live in the suburbs. Suburban communities, moreover, have a distinct geo-demographic identity compared to urban and rural areas, yet the government doesn’t really account for it! Compounding the problem is the slippery nature of the term “suburban.” It can mean different things in different parts of the country. 

All of this means that we have to define what suburban is ourselves. Marketing Systems Group’s geo-demographic team has developed their own definitions of suburban areas to compensate. 

Taking a simplistic approach, we take the census blocks within the principal cities of the MSA’s and keep them coded as “urban.” Any census block outside these principal cities that was classified as urban by the Census we now classify as “suburban.” On the other hand, any census block classified as rural by the Census remains “rural”.

Additionally, we can apply an urban/suburban/rural rule to any kind of geography or polygon. For example, we could take a ZIP code and classify it as urban, suburban, or rural. This is done by rolling up the underlining geography (census blocks) and determining whether the population (or land area) within a ZIP code is predominantly urban, suburban or rural. However, we could end up with a checkerboard affect with how the census blocks distributed across urban, rural, and suburban, so some care is needed.

We can also leverage our Addressed Based Sampling (ABS) frame to our advantage. Using ABS, we can identify population growth in areas in a shorter time frame instead of relying upon decennial Census data, which is only updated once every 10 years. If you are trying to define suburban areas, which can grow suddenly and dramatically, you will see how stale the data can become if you merely rely on decennial Census data. Using ABS gives you a more current, more accurate picture. 

For more insight, click here and check out Coffee Quip episode 8, Geo-demographic Methods: Suburban Geography, featuring Dennis Dalbey, Manager, Geo-demographic Services, and David Malarek, Senior Vice President, Sampling & Database Services. 

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Defining Small Area Geographies with Radius Sampling

In this blog we look at different ways to define small area geographies. How can we define a trade area or location using radius sampling (defining a geography around a particular point at different size ranges)? It sounds simple enough. You pick a point and draw a circle around the location. Done, right? Not exactly. The issue is how you identify geography within the circle. How precisely can we get at those addresses?

You can look at census blocks or block groups, or you can look at zip codes. It all depends on how large the radius is. Typically, we use census blocks for 5, 8, and 10 mile diameters, and because the blocks tend to fit well around the edges, we only need to do some minor carving.

With smaller radii, it becomes more of a challenge, though. Census blocks or block groups tend to fall way out of that range, or we get under coverage because not enough of the blocks or block groups fit inside the circle.

In episode 7 of our Coffee Quip video series, subject matter experts David Malarek (Senior Vice President, Sampling & Database Services) and Dennis Dalbey (Manager, Geodemographic Services) demonstrate the two basic ways to define radius geography using census blocks within a 10-mile radius—area inclusion using polygons and block centroids.

For example, we can start with a 10-mile radius around a point. Then we overlay census blocks (or block groups). On the overlay all block groups that intersect or have some relationship to the 10-mile radius can be seen. Where the color overlay falls outside the radius, we can decide which block groups to keep in or out of the sample frame.

The Polygonal Approach

By using polygon geometry, we can apply area inclusion. We can determine or make a cut on the percentage of the polygon area within the radii. For instance, any block group where the geographic area is at least 50% or more within the radius can be selected. When this is mapped, you will find holes along the edges of the circle where the geography once existed but was cut out because the inclusion was under 50%. Note that no matter how you carve the fringe, there will always be some overstatement of the sample frame or some under coverage depending on how well the block group geography fits the radius.

The Block Centroid Approach

Another way to do this is to use the center point of a polygon to assign geography to a radius. It’s a different type of geometry being put to use. Instead of using polygons where we’ll make an inclusion, we are actually using what’s considered the center of the polygon—the census block centroid. This method will allow us to select blocks that are theoretically 50 percent or more within the radii without having to apply an inclusion like we did with the polygon earlier. It is a more efficient way of doing it, but keep in mind that we are making a 50 percent cut across the board. You will encounter tradeoffs such as introducing under coverage or over coverage here, too.

One of the benefits of using the block centroid is that we can vary the distance. Let’s say we are not really sure whether the 10-mile radius is going to meet your quota. We may want to overstate the geography at 20 miles. With block centroid we can apply the distance and go from 10 to 15 to 20 miles until we meet the population or household quota. Note that this can be applied to polygons as well, but it is much easier to do with the block centroid.

The Address Level Approach

Yet another way to do this is to plot all the known addresses that fall within the blocks or block groups touching the circle and exclude any address that falls outside the circle. This is the most accurate way of getting accurate household counts and eliminates under and over coverage. It’s a two-step process and a more involved methodology but it is also the most accurate. One downside to this approach is demographic data is only available at some larger aggregation of geography such as block group and not by individual addresses.

Dave and Dennis compare the polygon and block centroid methods, and why they sometimes yield different results. Sometimes we actually need to plot ABS address locations in the blocks within the radius and remove the ones outside the radius, so we get a better fit for the overall target population. This is really the best methodology in terms of making sure that households are completely within a radius without having to worry so much about the regular geography, where part of it is in and part out.

Find more details and visualizations of these methods, in our Coffee Quips #7 video. It is the first in a series of geodemographic coffee quips. For additional information on our geodemographic services click here.

New Census ACS Data now Available. How Can MSG Help You Easily Gain Access to the Data?

New 5 Year American Community Survey Estimates Now Available

In mid-December, 2019, the U.S. Census bureau announced the availability of their 2014-2018 5-Year estimates, giving researchers cause to rejoice.  American Community Survey (ACS) is a heavily-used, “go-to” source for current social, economic, housing, and demographic information in the United States. The new 5-Year estimates are available for all geographic areas, reaching down to block-group level and include comparison profiles, subject tables, and narrative profiles. Continue reading “New Census ACS Data now Available. How Can MSG Help You Easily Gain Access to the Data?”

MSG’s Geo-Demographic Services are Critical Resources in Natural Disaster Preparation

Marketing Systems Group’s deep understanding of surveying and market research, coupled with our innovative products and services, have proven to be an invaluable resource to the survey research industry since 1987. 

MSG’s team, particularly our GeoDemographers, offer an array of services such as: Demographic Data, Reports, Maps, Geocoding, Spatial Analytics, Custom Geographic Frame Designs, and Census Information. Our GEO-DEM clients range from market researchers, public safety and emergency management, utilities and communications companies, health and human services, and transportation providers.   Continue reading “MSG’s Geo-Demographic Services are Critical Resources in Natural Disaster Preparation”

Why Location Continues to be a Difference Maker

Last Christmas I wanted to buy a turntable for my daughter. Thanks to an online message forum, I discovered that Target was selling a new brand of turntable at an affordable price point with features typically seen on higher-end models. It was early in the Christmas buying season, and I had a hunch that a product like this might sell out quickly. So I researched the Target.com website, checked their inventory and used the store locator to find the nearest Target with the turntable in stock. At this point many would click the “buy now” button and have the product shipped. Instead, I hopped in the car and drove to the store. Why, you ask? I wanted to see the product for myself before buying it. Once inside the store, my smart phone told me which aisle to go to. With a little help from my friend the store clerk, I located the turntable, looked it over, bought it, and wrapped it up for Christmas. What this very short story teaches us is that while technology has become a key component in the way we consume, we aren’t quite willing to let go of location-based purchasing decisions. Continue reading “Why Location Continues to be a Difference Maker”