Submitted by Harsha, who says:

I’ve been a big fan of your blog for over a decade. Recently, I had the opportunity to replicate the BART transit map for a data visualization in a story I wrote for the San Francisco Chronicle. I would love to hear your thoughts on it!

Transit Maps says:

First off, it’s great to see a transit map-related infographic from a newspaper graphics team! As an interesting and attention-grabbing way to present data, this is mostly succeeding, I think. Viewers of this map (and readers of the accompanying article in the Chronicle) in the Bay Area would almost certainly be familiar with the BART diagram, allowing them to quickly relate the data shown to their mental image of the system and the Bay Area as a whole.

That said, much the same information could be obtained from a standard temperature map of the area like you’d see on the evening news (see left). This is especially true when you consider the methodology of coming up with the temperatures as shown – the Chronicle article makes it clear that the temperatures are obtained by a model that uses a conglomeration of different sources for each general area with “computed values… for areas about 1.5 miles in length and width.” So, if you were thinking that the temperatures were actually recorded at each station on the BART system, you’d be wrong. This generalised model probably also doesn’t take into account the fact that many of the inner stations are underground, which would almost certainly further affect the temperature at those stations.

So what we really have here is a dataset of general temperatures in the Bay Area which is simply using the BART diagram as the medium for conveying that information, rather than a diagram of actual temperatures within the BART system itself – which may be what readers are expecting given the context. Finally, the general conclusions from the data – that it’s cooler nearer the coast and San Francisco’s well-known marine layer, and hotter inland away from that influence – aren’t exactly surprising.

Design-wise, the graphic obviously draws its cues from the official BART diagram, which helps add familiarity for the viewer. An interesting side-effect of showing all the separate route lines – even though it doesn’t really add useful information in this context apart from being familiar – is that the areas where three or four route lines run concurrently get more “surface area” for their colours to show, so they tend to be more visually dominant. The eye is drawn to that big teal/green area in San Francisco and kind of skips over the hottest part out to Antioch, which only gets a single line’s width worth of colour. An alternative approach might be to just have one slightly thicker line for all the branches rather than retaining all of the separate routes, though this does sacrifice some of that instant recognition.

The diverging colour palette is very appropriate for the type of data being shown and looks great, especially when used as gradients along the route lines. Perhaps it could be a little more optimised for colour-blind users – the middle values all look pretty similar in my simulations – but the general trend of cooler colours to the left and warmer colours to the right does a decent job, really. Some people might also take issue with the legend being broken up into discrete values when the data on the map is a continuous gradient, but it works for me as I think you can quickly understand the data range better this way.

Lastly, a little more care with the labelling of stations would have been good. The labels from Civic Center up to Embarcadero get progressively further and further way from their corresponding stations, and there’s more than a few inconsistencies like that across the graphic.

Our final word: A fun and memorable way to present information in a digestible, bite-sized chunk, which is the hallmark of good newspaper graphics. However, the graphic might not be representing exactly what people are expecting given the context of using the BART diagram to deliver the information.

Source: @HarshaReports/Twitter