The first set of methods that we have to cover that pertain to changes in the view are the following. We have selection, navigation and spatial arrangement. Let's start with selection, what is selection? Well, selection is any action any interactive action that you make that is aimed at selecting one or more elements in your visualization and typically these elements can be either items and or attributes from the dataset. So, in the videos that I've shown you previously in the animations or demos, you have already seen a lot of examples of selections. So, when I select some dots in the scatter plot, that is a selection of a group of food products. When I clicked on one of the bars I selected one group of products and so on. So, in general these interactive visualizations and interfaces enable the selection of one or more elements on the screen. Now, it is important to keep in mind here that typically there is an action in something that changes or you can also see that as an input from your device and an output and a reaction in the visualization. So, what we have to cover now is what actions can happen on the screen and through your interactive devices and what changes can happen as a reaction to this input. So, we typically have three main types of actions in current visual interfaces. This is by no means exhaustive, but these are by far the three most common type of actions that you will see in an interactive visualization application. So, the first one is just a simple click, so you click on some elements on the screen and you select it. The second one is hovering, which is the one that we have seen on the scatter plot, example, you hover over the elements with your mouse and as you get closer, close enough to appoint something happens, in that case we had a pop up label showing up. But we can also have types of selections that enable you to select groups of elements. So, for instance if you click and drag and select an area, then you can select and draw an area, then you can select all those elements that are underneath the area that you just created with click and drag. So, this is important to keep in mind because there are many different ways to make selections and typically people have expectations about what interactive methods are available for selection. So, one important note here is that, you should almost never break the defaults or what people are expecting you to implement in your visualization as a way to make selections. So, it's good advice to check how selections are implemented in other systems and try to go with the most common way of making selections. Another thing to keep in mind here, is that selection can be about single items or groups of items. What we have to see next is what happens once the selection is made and here there are a number of options which I'm going to show you in the next video.
