ArcGIS Pro

Time Warped Cartograpy

Here is a ridiculous walking distance map of Seattle. The geography of areas accessible via a 1, 2, and 3 hour stroll are warped into concentric rings. While it looks like an ice cream cone on a hot day, its actually a pretty practical map -if you’re a pedestrian.

 

What’s Real?

If our reality is walking, which it often is, then this is the most realistic look at Seattle going. It’s a reminder to me that all maps are a compromise between literal spatial reality, our practical spatial perceptions, and the map reader’s goals. Maps are just little communication devices, and I need to ask myself all the time, what is the most important purpose of this map? It’s always a tightrope between a sense of precision and the message that a map carries to its reader. It can be easy to fixate on the former at the expense of the latter. I like this time warp map because it’s an especially inflated example of that. Like Gallagher and a watermelon.

Where Did It Come From?

In 2011, in a brightly lit little office in the Geography building of Michigan State University, Kirk Goldsberry showed me a yellowed old draft manuscript of Waldo Tobler’s (covered in his hand-written notes; it was awesome) in which he’d diagrammed a map of Seattle this way. I always wanted to try it but wasn’t sure about how.

At some point it occurred to me that I could hijack the georeferencing feature to warp, like a rubber sheet, totally unsuspecting isochrons into these rings. I don’t know how other people do it, but this could work for a guy like me.

How To?

Like many things I make, this is the result of an absurd use of a perfectly well-meaning tool. Wait, is that true? Is that what I’m doing?

Deep breath Nelson. Push that existential crisis down to your feet. Ok. Ok, we’re good.

Ah-hem. Pardon me. Here’s how it goes:

  1. Create Walk-time service areas in ArcGIS Pro.
  2. Export 2 mega-huge images of the Seattle area (one with the service areas baked-in and one without).
  3. Create equal-distance rings roughly overtop the service areas (multiple ring buffer, matching the number of service areas).
  4. Add the image with the service areas as a layer.
  5. Using the georeference tools, warp the service areas to the equal-distance rings via a kajillion control points (spline method).
  6. Save the control point table and apply them to the image of Seattle without baked-in service areas. And save it as a new, time-warped image!

As always, I find that pictures help…

Here are three walking “service areas” from a dot I dropped downtown, created using the Generate Service Areas tool.

In a really big layout, I export two high-res images. One image has these service areas baked into it (I’ll use it as a reference to create control points) and the other is just sweet sweet imagery (I’ll use this as the image that I ultimately georeference).

Next I created three rings or equal distance around the walk origin point using the Multi-ring Buffer tool. The distance was somewhat arbitrary, so long as they are all equal.

Then I add the exported image with the service areas baked into it back into the project as a dumb, non-geographic image. Time to get warping!

The Georeferencing toolset in ArcGIS Pro rules. You just set a bunch of control points connecting a pixel on the image to a real-world coordinate. Click/clack, click/clack, click/clack. I chose the Spline warping method. Spline gives you an absolute pinning of control points, but you need at least 10. No problem; I ended up with like 150 control points. Click here to see a fun animation of the warping.

When my service area polygons were sufficiently warped to my rings, I exported the control points table (it saves it as a .txt file with all the origin pixel coordinates and destination geographic coordinates). I don’t actually need to save a warped version with the service area lines. I want to have a warped image without those reference lines.

So, I cancelled that geoprocessing session (since I had saved my control points table), and added in the big high res image without the service area lines. And that’s the image I ended up applying the control points to. Bait and switch. Thank you for your service, service areas –we’ll take it from here.

I saved the image, all time-warped up, and took it into a new Layout for decoration. And that is that.

Happy Warped Mapping! John

About

I have far too much fun looking for ways to understand and present data visually, hopefully driving product strategy and engaging users. I work in the Content team at Esri, pushing and pulling data in all sorts of absurd ways -and then talking about it. I also get to spend time with the Story Maps team, working on fun and useful user experiences. When I'm not doing those things, I'm chasing around toddlers and wrangling chickens, and generally getting into other ad-hoc adventures. Life is good.

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