Now, I want to focus on another important aspect of visualizing a large set of timelines. This is about scalability. So, how do you visualize a very large set of timelines? As we have seen at the beginning of this lesson, if you use line charts. Once, you try to visualize more than a handful, the visualisation tends to be very, very cluttered. So, it doesn't work really well. On the other hand, if you use any of the other techniques that have presented so far. Like for instance, heatmaps or calendar like visualizations, they do scale a little better, but they also have limitations. Right. As the number of elements increases, the objects get smaller. So, it becomes really hard to observe temporal patterns. So, how do you actually make timelines visualizations more scalable? Well, there is actually two techniques that I want to talk about. The first one is the horizon chart. So, what is the horizon chart? So, let me walk you through a number of steps. First of all, look at this visualization. This is a visualization where we are trying to visualize, a lot of timelines at the same time. As you can see, there is not much that you can extract out of this visualization. Why? Well, because we are trying to use a line chart in a very small space. So, there is not enough space, enough resolution to see a lot of changes in such a long timeline. So, the horizon chart, tries to address this problem as follows: So, starting from a line chart like this one. What you have to do, is to first segment the line chart into enough number of bands as you can see here. You color with the one colored those that are above zero or the average of the timeline and with another color those that are at the bottom. Not only that, we deem this two use, the one that you have at the top and the one that you have at the bottom, you can also use different color intensities to represent the actual band. So, those that are closer to zero or the average are lighter, and they get darker and darker as they go far away from the centre. Now, that's the first step. The second step, is to take those that are at the bottom and flip them so that, now all of the segments are on one side of the timeline. Now, you need another step for all the bands that have been created, you can now collapse all of them and stack them together, as you can see in this image. So, this is a crucial step and once you do that, you get the horizon chart. A very scalable and very effective visual representation of a very large set of line charts. So, what is interesting here is that, there is a combination of visual solutions to make line charts much more scalable visually. So, part of it is using color effectively, but part of it is also this idea of stacking together different segments of the timeline, so that you can still see a shape within a shape. The second technique that I want to talk about is sparklines. So, sparklines have been introduced by Edward Tufte, in his most recent book called Beautiful Evidence. He defines sparklines as follows "So, there are small, intense, word-sized graphics with typographic resolution. Sparklines can be placed anywhere that words or numbers or graphics can be placed: in sentence, maps, graphics and tables". So, what is the idea here? The idea here is that you can create timelines that are so small, that they can be placed within text or in context of documents that contain a lot of other elements. So, the crucial intuition here is that, timelines if they are designed effectively, they can still visualize a lot of interesting patterns even when they are very small. This is a very interesting phenomenon in visualization, that it takes a while to appreciate. There are lots of interesting patterns that we can still discern, even when we make these visualizations very small. That's the main idea behind sparklines. So, these are some examples of use of sparklines. So, typically sparklines don't have access, don't have lots of labels and don't have lots of grids so that, you can only see what is going on in a timeline in comparison to the other timelines. So, they are very effective when they are placed in a document, as I said earlier. This is an example that you can see on the left and since they are still effective when they're very small, they can also be used in any other situation where we don't have a lot of space to represent data. On the right hand side you see another possible example, where this is used in watch like the one that I have here. Very small representation can still be very effective. So, remember: these two methods as a way to scale up, in terms of space and quantity horizon charts and sparklines.
