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October 28, 2016

Filed under: journalism»new_media

How I built the ST3 guide

On election day, voters in the Seattle metro area will need to choose whether or not to approve Sound Transit 3, a $54 billion funding measure that would add miles of light rail and rapid bus transit to the city over the next 20 years. It's a big plan, and our metro editor at the paper wanted to give people a better understanding of what they'd be voting on. So I worked with Mike Lindblom, the Times' transportation reporter, and Kelly Shea in our graphics department to create this interactive guide (source code).

The centerpiece of the guide is the system map, which picks out 12 of the projects that will be funded by ST3. As you scroll through the piece, each project is highlighted, and it zooms to fill the viewport. These kinds of scrolling graphics have become more common in journalism, in part because of the limitations of phone screens. When we can't prompt users to click something with hover state and have limited visual real estate, it's useful to take advantage of the most natural verb they'll have at their fingertips: scroll. I'm not wild about this UI trend, but nobody has come up with a better method yet, and it's relatively easy to implement.

The key to making this map work is the use of SVG (scalable vector graphics). SVG is the unloved stepchild of browser images — badly-optimized and only widely supported in the last few years — but it has two important advantages. First, it's an export option in Illustrator, which means that our graphics team (who do most of their work in Illustrator) can generate print and interactive assets at the same time. It's much easier to teach them how to correctly add the metadata I need in a familiar tool than it is to teach the artists an entirely new workflow, especially on a small staff (plus, we can use existing assets in a new way, like this Boeing retrospective that repurposed an old print spread).

Second, unlike raster graphic formats like JPG or PNG, SVG is actually a text-based format that the browser can control the same way that it does the HTML document. Using JavaScript and CSS, it's possible to restyle specific parts of the image, manipulate their position or size, or add/remove shapes dynamically. You can even generate them from scratch, which is why libraries like D3 have been using SVG to do data visualization for years.

Unfortunately, while these are great points in SVG's favor, there's a reason I described it in my Cascadia talk as a "box full of spiders." The APIs for interacting with parts of the SVG hierarchy are old and finicky, and they don't inherit improvements that browsers make to other parts of the page. As a way of getting around those problems, I've written a couple of libraries to make common tasks easier: Savage Query is a jQuery-esque wrapper for finding and restyling elements, and Savage Camera makes it easy to zoom and pan around the image in animated sequences. After the election, I'm planning on releasing a third Savage library, based on our <svg-map> elements, for loading these images into the page asynchronously (see my writeup on Source for details).

The camera is what really makes this map work, and it's made possible by a fun property of SVG: the viewBox attribute, which defines the visible coordinate system of a given image. For example, here's an SVG image that draws a rectangle from [10,10] to [90,90] inside of a 100x100 viewbox:

If we want to zoom in or out, we don't need to change the position of every shape in the image. Instead, we can just set the viewbox to contain a different set of coordinates. Here's that same image, but now the visible area goes from [0,0] to [500,500]:

And here's one where we've zoomed in on the lower-right corner, by viewing a 40-unit box starting at [60,60]:

Savage Camera was written to make it easy to manipulate the viewbox in terms of shapes, not just raw coordinates. In the case of the ST3 guide, each project description shares an ID with a group of shapes. When the description scrolls into the window, I tell the camera to focus on that group, and it handles the animation. SVG isn't very well-optimized, so on mobile this zoom is choppier than I'd like. But it's still way easier than trying to write my own rendering engine for canvas, or using a slippy map library like Leaflet (which can only zoom to pre-determined levels).

This is not the first time that I've built something on this functionality: we've also used it for our Paper Hawks and for visualizing connections between Seattle's impressive women in the arts. But this is the most ambitious use so far, and a great chance to practice working closely with an illustrator as the print graphic was revised and updated. In the future, if we can polish this workflow, I think there's a lot of potential for us to do much more interesting cross-media illustrations.

Future - Present - Past