Tags: dataviz



Month maps

One of the topics I enjoy discussing at Indie Web Camps is how we can use design to display activity over time on personal websites. That’s how I ended up with sparklines on my site—it was the a direct result of a discussion at Indie Web Camp Nuremberg a year ago:

During the discussion at Indie Web Camp, we started looking at how silos design their profile pages to see what we could learn from them. Looking at my Twitter profile, my Instagram profile, my Untappd profile, or just about any other profile, it’s a mixture of bio and stream, with the addition of stats showing activity on the site—signs of life.

Perhaps the most interesting visual example of my activity over time is on my Github profile. Halfway down the page there’s a calendar heatmap that uses colour to indicate the amount of activity. What I find interesting is that it’s using two axes of time over a year: days of the month across the X axis and days of the week down the Y axis.

I wanted to try something similar, but showing activity by time of day down the Y axis. A month of activity feels like the right range to display, so I set about adding a calendar heatmap to monthly archives. I already had the data I needed—timestamps of posts. That’s what I was already using to display sparklines. I wrote some code to loop over those timestamps and organise them by day and by hour. Then I spit out a table with days for the columns and clumps of hours for the rows.

Calendar heatmap on Dribbble

I’m using colour (well, different shades of grey) to indicate the relative amounts of activity, but I decided to use size as well. So it’s also a bubble chart.

It doesn’t work very elegantly on small screens: the table is clipped horizontally and can be swiped left and right. Ideally the visualisation itself would change to accommodate smaller screens.

Still, I kind of like the end result. Here’s last month’s activity on my site. Here’s the same time period ten years ago. I’ve also added month heatmaps to the monthly archives for my journal, links, and notes. They’re kind of like an expanded view of the sparklines that are shown with each month.

From one year ago, here’s the daily distribution of

And then here’s the the daily distribution of everything in that month all together.

I realise that the data being displayed is probably only of interest to me, but then, that’s one of the perks of having your own website—you can do whatever you feel like.

Canvas sparklines

I like sparklines a lot. Tufte describes a sparkline as:

…a small intense, simple, word-sized graphic with typographic resolution.

Four years ago, I added sparklines to Huffduffer using Google’s chart API. That API comes in two flavours: a JavaScript API for client-side creation of graphs, and image charts for server-side rendering of charts as PNGs.

The image API is really useful: there’s no reliance on JavaScript, it works in every browser capable of displaying images, and it’s really flexible and customisable. Therefore it is, of course, being deprecated.

The death warrant for Google image charts sets the execution date for 2015. Time to start looking for an alternative.

I couldn’t find a direct equivalent to the functionality that Google provides i.e. generating the images dynamically on the server. There are, however, plenty of client-side alternatives, many of them using canvas.

Most of the implementations I found were a little heavy-handed for my taste: they either required jQuery or Processing or both. I just wanted a quick little script for generating sparklines from a dataset of numbers. So I wrote my own.

I’ve put my code up on Github as Canvas Sparkline.

Here’s the JavaScript. You create a canvas element with the dimensions you want for the sparkline, then pass the ID of that element (along with your dataset) into the sparkline function:

sparkline ('canvasID', [12, 18, 13, 12, 11, 15, 17, 20, 15, 12, 8, 7, 9, 11], true);

(that final Boolean value at the end just indicates whether you want a red dot at the end of the sparkline).

The script takes care of normalising the values, so it doesn’t matter how many numbers are in the dataset or whether the range of the numbers is in the tens, hundreds, thousands, or hundreds of thousands.

There’s plenty of room for improvement:

  • The colour of the sparkline is hardcoded (50% transparent black) but it could be passed in as a value.
  • All the values should probably be passed in as an array of options rather than individual parameters.

Feel free to fork, adapt, and improve.

The sparklines are working quite nicely, but I can’t help but feel that this isn’t the right tool for the job. Ideally, I’d like to keep using a server-side solution like Google’s image charts. But if I am going to use a client-side solution, I’m not sure that canvas is the right element. This should really be SVG: canvas is great for dynamic images and animations that need to update quite quickly, but sparklines are generally pretty static. If anyone fancies making a lightweight SVG solution for sparklines, that would be lovely.

In the meantime, you can see Canvas Sparkline in action on the member profiles at The Session, like here, here, here, or here.

Update: Ask and thou shalt receive. Check out this fantastic lightweight SVG solution from Stuart—bloody brilliant!