Let's go back to the key concepts. The first one is that we are talking about Computer-Based visualization. As it may be more obvious now after the demo, we're talking about visualizations that are created by a computer. The second one is that we are talking about Visual Representations. Obviously since this is about visualization in general, we are talking about visual representations that are created from data via computer. The next one is a little trickier. Abstract Data. What does it mean? Well, first of all it means that we are talking about representing visually data that doesn't necessarily have a very natural or obvious visual representation. One way to think about it is to think about the difference between visualizing physical data or physical objects or phenomena versus data that is not necessarily physical. So, here for instance, I'm showing visualizations that represent some physical phenomena or object. The one on the left is a representation of a human skull, the one on the right, is the representation of some weather data. In both cases, we are visualizing physical phenomena and what happens is these cases is that in the large majority of cases, we have an obvious or somewhat obvious way of visualizing this data. Not only that, the second point is that in these visualizations, realism is a good thing. Trying to create a visual representation of the phenomenon in a way that is as close as possible to the phenomenon or the object itself is an important goal. But, when we are using abstract data, data that describes objects or phenomena that are not physical things get a little harder. So, let's talk about another example. In this spreadsheet, you see data that I have personally collected in a personal project that I developed a few months back. In this project, I have been collecting personal information about the times when I work, long I work for, what is the project I'm working on and some other information. So all this information is collected in a spreadsheet but when you start thinking about it, it is not very obvious how to visualize this information, is not physical phenomenon. For instance, how do you visualize time? How do you visualize the concept of duration or project name? Or type of activity, et cetera. So, this is when one of the major issues in information visualization. In most of the cases, there is no obvious visual representation and you as a visualization designer have the very hard task to decide what's the best representation for something that is abstract.