Another option available when you have high number of timelines is to use what is called a small multiples line charts. What is a small multiples line chart? Well, the idea is that, rather than using one single line chart and have the lines overlap, you can make much smaller graphs and repeat the graph multiple times as many times as the number of lines that you have or objects or categories that you want to represent, like the one that you see here. The general-purpose technique that you can reuse with any other graph is called the small multiples, but in this case, we talk about the use of small multiples to represent different timelines. So, what are advantages and disadvantages of these solution? Well, one advantage is that you have much, much less clutter because the lines don't overlap, but the disadvantage is that comparing them becomes harder for two reasons: one, because they are no longer in the same chart and second, because they are smaller. There are situations though where small multiples line charts are really, really powerful. In particular, if your goal is not necessarily to compare across the lines, but more to show for each of these categories or objects what the actual trend is, then small multiples timelines is a very, very powerful solution. A little variant that you can use on small multiples line charts is to use what is called area charts, like the one that you see here. So, that's with lines and that's with areas. What is the difference? Well, the only difference is that all the area below the line up to the axis is filled up with color. The reason why this works particularly well is because when you fill it up with color, then it's easier for our eyes to perceive the shape. This is even truer in the case of small multiples line charts because the plots becomes smaller and smaller. The smaller they are, the easier it is to perceive the shape using an area. Since we are talking about area charts, we now can also talk about another very common kind of graph that is the stacked area chart, like the one that you see here. So, what is a stacked area chart? Well, the idea here is to represent the proportion of something over time. So, here again, I'm using the same data as before. We have time on the x-axis, we have the amount of sales on the y-axis, and here for four different regions in the US. So, Central, East, South and West. So, what can you see in this chart? Well, you can see the overall amount of sales, which is given by the outer shape of the area chart. But you can also see the proportions of each area, which is given by the width of each of these colored lines. Now, area charts are one possible tool that you can use when your goal is to represent proportion of something over time. One thing to keep in mind though is that it's not always easy to understand what an area chart represents. I would also say that it's easy to mislead because what our eyes tend to do when we are looking at an area chart is to interpret the actual temporal pattern of each of these bands as if it was meaningful. But it turns out that this pattern is not necessarily meaningful. Why? Well, because the shape of each band represents on the actual shape of the time series that you have at the lower level of this time band. So, the only thing that counts is the actual width of these band but not the shape. So, our eyes tend to focus on the temporal trend, but what really matters is only whether the width of this line changes over time or not. So, one way to see that is by comparing these two graphs that you see in front of you. Once again, this is exactly the same information. The only difference between the two is that the one on the left is stacked area chart where the time series are stacked together to show the proportion, whereas the one on the right-hand side is actually just timelines. As you can see, if you look at the trends, they tend to be very, very different. But this is not apparent when you look at the same data in a stacked area chart. One way to mitigate this problem is to use what is called a percentage or percent area chart. So, in this chart, the difference is that on the y-axis, rather than having the actual amount, we have percentage. As you can see, this more directly represents the idea that the values that you see there should be interpreted as percentage of something. So, this mitigates the problem of stacked area charts. So, I think it's important to introduce this graph because it's very common to see it, but I would urge you to be very careful in using it because it's very common for people to mislead or misinterpret the information that is conveyed with this kind of visual presentation.