The culprit’s name is “Web Mercator”! So the map projection Tableau uses to display maps is raining on our parade. And worst of all: they don’t all look the same! But looking at them, or rather their geographic distribution, already gives us a hint at what might be going on here. You can find some details about how to get that data, what’s in there and some necessary preprocessing steps in that first article.Īssuming you’ve done all that, let’s see what happens if we apply the logic we developed for scatterplots on a map: So back to the super cool data which I have already used in my blog post on visualizing paths in Tableau and also in another context when writing about the new great circles feature in Tableau with Sarah over on the Tableau blog. Now it’s finally time to use some interesting, real-world data, that actually makes sense, and also proves my point that multiplying the data six times doesn’t even make Tableau break a sweat. So, in the last article we worked with a very small dataset that helped us grasp what was going on with the data in all the numerous Calculated Fields (there’s 14 of them, actually). Sarah is an absolute expert on all things map projection, as she has shown time and time again in articles on the topic on the official Tableau and Tableau Public blogs and elsewhere (as in: real scientific publications). All original work was done by Alan Eldridge and the herself, Tableau’s Sarah Battersby in an article on hexbinning on Alan’s blog back in 2015. While I claim the arrows to be my original idea (at least I didn’t find anything similar on the web – please correct me if I’m wrong!), I can’t and won’t take credit for this one. This article shows how these difficulties can be overcome using some on-the-fly reprojection of our data. The approach introduced there – I dubbed it the “linear” approach, as instead of drawing one line we created two additional lines for the arrowheads – works fine on scatterplots, but things turn out to be a bit more difficult when working with maps. This is the continuation of a blog post I published a few weeks ago on how to draw directed arrows in Tableau.
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March 2023
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