Okay. Now, let me give you a few examples of how to express quantity with different channels. We will start with the first one, which is position. So, imagine that we have one axis, like this, and the position of an object on this axis can express a quantity. A very similar situation you might be more familiar with is when I have a pair of axis, like this one orthogonal axis, and the position of one dot would actually represent the two quantities at the same time. This is exactly the technique that is used when one creates a scatter plot. Okay. One can express quantity also using size. So, for instance, the size of bubbles, like in this case, the area can be used as a channel to convey information about a quantity. The same can be done, for instance, with the length of bars. This is what you find in bar charts. The length of a bar expresses information about a quantity. Another channel that we can use is angle. So, one way to show that is, for instance, the angle of pizza slices, like this one. So, this one has a bigger angle than this one. So, B is bigger than A, for instance. But that's not all, we can also use a slope for direction. So, if I draw two lines, one like this and one like this, so these two lines can express the direction and slope of these lines can express quantity, and you can very readily see that this one here is steeper than this one here. Last one that I want to show you is color intensity. So, if I have patches of color, like this ones. So, this is clearer, this is darker, and this is even darker, so the intensity of colors can also be used as a way to express a quantity. So, in summary, we have position, size, note that size can be expressed in many different ways. So, here, for instance, we used area size but also length of bars, then we have angle. So, for instance, in pie charts, angle is used together with other channels to express, together with area to express a quantity, then we have slope. For instance, this is used in line charts to express information about how quickly something changes over time. Finally, we have color intensity. Color intensity.
