The next method that we need to cover is spatial arrangement and this is the last method that belongs to the class of methods that change the view. So, what is spatial arrangement? Spatial arrangement is any interaction that changes the arrangement of the objects on the screen. In particular, a very common and very powerful type of rearrangement is reordering. So, it is very common in visualization to have different ways to reorder the objects that are displayed on the screen in a way that it enables the viewer to pursue different types of questions. Let's start with a very simple example. Even with a simple bar chart like the one that you see here, we always have at least three types of possible orderings. The first one is alphabetical ordering, the second one is descending by the values that are displayed on the bars, and ascending values. So, each of these three types of ordering are very useful. So for instance, alphabetical ordering is very useful if I'm looking for some specific labels. Descending ordering is useful if I want to know what are the top X elements, say the top five or ten elements. The same is true for ascending. If I want to know what are the bottom X elements, then I can reorder the list or the bar chart by the value and see what are the bottom ones. So, the interesting thing is that all these questions are very useful at the same time. I may want to look at a specific label, so use alphabetical order or at the top values or at the bottom values. Interaction plays a major role because I can just click on a button or change an option in the user interface and change the ordering of the bar chart and pursue different questions at the same time. So, that's another reason why interaction and this specific kind of interaction is very useful. So, I'm going to stop here and in the next two videos, I'm going to show you two examples of visualization systems that make heavy use of reordering as a way to pursue complex analytical problems.