The next interaction method that I want to introduce is navigation, which is another way to change the view. What is navigation? Well, the basic idea of navigation is that we may want to interact with the visualization so that we can change the level of details at which something is represented. So we may, for instance, zoom in or zoom out. Or we may want to move the viewpoint of the visualization so that we can observe parts of the visualizations that are currently hidden by the view. So by far, the most common navigation method is zooming and panning. So zooming is going in to the details of a visual representation, or zooming out. And panning is moving the visualization in the view port so that you can see hidden areas and navigate through the space of the visualization. So now I want to give you an example of zooming and panning, and I want to use a familiar example. The familiar example is Google Maps. I'm pretty sure that many of you have used Google Maps or some similar services. And Google Maps is an excellent example of zooming and panning. So what you see here is the map of Brooklyn at a certain zoom level. This is actually centered where our school is. And in Google Maps, you have these interaction tools, these widgets that you can use to zoom in into an area or zoom out from these areas. So if I click here, I can zoom in, and if I click here, I can zoom out. If I drag the map, I am panning the map and moving, navigating through this visualization so that I can see areas that were previously hidden. So I can zoom in, I can move. I can zoom out, and I can move. So now I want to briefly introduce another very important concept, the concept of semantic zooming. So what is semantic zooming? The idea is that when you zoom in or out in a visualization, you may do it in two different ways. You can have geometric zooming that just scales everything up or down according to the zoom level, or you can have semantic zooming. Semantic zooming, the basic idea behind semantic zooming is that what information is presented at a given zoom level, and at what level of detail changes with that zoom level. And I don't know if you've ever noticed that, but this is what happens in Google Maps, as well as many other zooming systems, systems that contain zooming capabilities. So if you observe in this map, you will see that, for instance, at this distance if you focus on the little sign with a M on top, these are actually the subway stops in this region. But you will notice that there's no name next to these subway stations. But when I zoom in, now the names pop up, and the same is true for many other elements. We probably do not notice it because it's very natural. But if you start noticing it, you will see that according to the zoom level there are pieces of information that become apparent or disappear when you zoom out. So another good example here is the name of the parks. Not all the parks have a name. But if I zoom in, now I have names for all of the parks. And the same is true for name of the streets or also which streets are shown. If I zoom out, there are less and less details that are shown. So this is what is called semantic zooming. And zooming and panning is a very general purpose method to navigate in a visualization system. So it's almost always true that our visualization can be enhanced with zooming and panning capabilities so that the user can navigate the data space represented by the visualization.
