Where are Washington, DC’s most interesting places? On the theory that people are more likely to take photos of interesting places, I used Flickr’s API to find out how many photos were geo-tagged across the region. Starting with a 480-by-360-pixel map, I created a grid with 32 columns and 24 rows, making 768 15-by-15-pixel squares. For each square, I calculated the latitude and longitude of the boundary, and asked Flickr to tell me how many photos have been geotagged in that area. The cropped image below makes it clear the National Mall is the most-photographed place in the area, with West Potomac Park and downtown also registering on the radar.

That bright red square on the Mall has 63,793 photos taken on it, but the total for the original (uncropped) map has 719,633. I used a linear scale to set the opacity of each square in the heat map. Any square with fewer than 1% of the highest-value square’s total will be practically invisible. Since the Mall dominates the photographic landscape, I need to use a different display method to show the variation among the less-popular areas.

The map below uses two linear scales to translate the numbers into colors. For squares with less than 1% of the max square’s total, they are drawn in blue, using their transparency to reflect their value. Squares in the top 99% use a scale that has the max opacity, but changes color from blue to cyan. The 1%-99% split is arbitrary, and there is no way to indicate to the viewer where the split is taking place (without a key). I experimented with other values and thought this combination looked best. This two-tone method hides how much the Mall dwarfs other areas, but lets us better see patterns beyond the Mall.

I then tried using a logarithmic scale to distort the numbers to make the smaller values visible. Using the natural logarithm, I got the following image, which to me squishes the data too much, and makes it harder to discern the true highlights.

I prefer to use the two-tone map (in blue) for analysis. It shows us that we have very few geo-tagged photos on Flickr east of the Anacostia River. Prince George’s County is mostly blank except for College Park, and smaller blips for FedEx Field and Andrews Air Force Base (which is open to the public for the annual Joint Service Open House and Air Show). In Montgomery County (Maryland), Bethesda and Silver Spring have their own clusters. There is also a significant blip for Glen Echo Park near the Potomac River, in the northwest corner of the map. Virginia has a large cluster in Arlington, with a smaller cluster in Old Town Alexandria.

The Flickr heat map is a good tool to analyze areas that have a lot of photos taken.

next: Zooming in on Neighborhood Heat Maps

Washington through the Eyes of Flickr

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