There Are 1.75 Mil. People Inside the Beltway & Cool Maps

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Population by Census Tract

I noticed the Inside the Beltway geography is often not explored an isolation, so I’m here to provide some cocktail-hour conversation starters. People often show stats about the District of Columbia, but as an urbanist I tend to think of things in terms of the “functional city.” The Metropolitan Statistical Area is often one definition, and there are countless others, as to what a “functional city” means, but lets look at the DC functional city as Inside the Beltway.

I calculated some statistics for you, and here’s the main one you’re wondering about: there are 1.75 million people inside the Washington Beltway. I also made some interesting maps for you folks.

Method

By inside the beltway, I mean exactly that: the are inside the I-495 beltway that surrounds Washington, DC. This excludes areas like Tyson’s Corner (but not my neighborhood, Pimmit Hills, just inside the Beltway!), Reston, and parts East in Prince Georges County.

The way I did this was to get the Census Tract TIGER shapefiles from the US Census. I used the ArcGIS trace tool to only select the census tracts that are within the beltway. Finally, I tied this to 2011 ACS 5-year population estimates to get our statistics.

To calculate density, I had to calculate the land area. I got the total area, did some water shapefile manipulation (merge, clip, etc). Eventually subtracted out the water area, also using Census TIGER files. That way we know the land area.

And for those of you who keep score at home, for break points in the visualizations, I used 7 “natural breaks” categories for each of the maps.

Population Stats Overview

Again, I’m literal: Inside the Beltway. And here are the statistics for the Inside the Beltway area, and how it compares to other cities.


Population Map

(note: map doesn’t work on mobile browsers)

By population, you can see that the area is rather dispersed throughout. This isn’t a big demographic analysis here, and I’m just giving you a nifty tool using ESRI Online maps. Take a look around, explore, and see some of the population trends.



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Density Map

(note: map doesn’t work on mobile browsers)

I’m anticipating people saying, “hey, Mike, what about density?” Well, here is that map too. As you see, we have strong density where you expect, especially along the 15th and 16th street corridors in DC, and in NW DC overall.

As far as some of the other standouts, we have the area around College Park, the Arlington / Clerndon Blvd. corridor, areas near Georgetown, and some more obvious spots.

Crowdsource project! Can some of you folks explain some of the more “random” standouts. I’m looking at you, area near Seminary Rd meets I-395!



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Conclusions

U can has maps! Have fun. Enjoy. Learn. Comment. And share!

If you want me to share data with you, or provide you off-line versions of these maps, contact me through your social media method of choice.

**UPDATE**

I corrected the area of the geometry inside the beltway to 265.8 sq. mi. Some commented to me that over 400 sq mi. seemed big, and I agreed. I fixed it, and it was a projection issue. I was projecting the shapefile using WGS Web Mercator (Auxiliary Sphere), instead of a much more appropriate State Plane. I used State Plane Maryland for the new projection and got much more accurate area measurements. My bad. FYI: watch your projections when using distance/area measurements in ArcGIS. :)

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