This process of mapping the real world. One of the options we have is to use the vector data model in order to take reality and turn it into a simplified version to put on our map. So, let's have a closer look at the vector data model. So, here we have the island of Hawaii, and we're depicting certain things on here using the vector data model. So, if we look at the legend, we have emergency shelters and volcanoes being shown as points, highways lines, and lava flow hazard zones as areas or what we would refer to from a vector point of view as polygons. So, here's our points, here's our lines, here's our polygons. It's not a coincidence by the way that the points are on top in this legend. The lines are in the middle, and the polygons are on the bottom. So, this actually relates to the drawing order that used by the software when it's creating this map, is that you want the polygons that covered the most area to be on the bottom. Then the lines would go on top of that, because if you had the lines underneath, if you had these down here, then you wouldn't be able to see them because the polygons would be on top, and the same thing for the points. So, the software by default will actually put the points on the top, lines below that, and polygons below that. You can move them around. You can put them in whatever order you want. You can make them semi-transparent. We'll talk about symbology in another section, but that's a starting point, and it's kind of if you have no other reason not to do that, it's a good place to start from. We can associate that attributes with each of these locations. So, these are the attributes for this. So, for volcanoes, you'll see that we have a volcano here that's being shown as a point there. We have Mauna Kea here. Mauna Kea is up there. So, the vector data model is not just about showing something on the map, it's also connecting that to data in a table that's associated with that point, or line, or polygon. So, just to make sure this is clear, points have zero dimensions. That is, that there is no length or width. They infinitely small, and regardless of how big the symbol is, that's just how we represent it. So, that doesn't mean that it's taking up that much space on the ground. In the terms of the software and how it treats it, that point has no dimensions. Lines have one dimension, so that is that they have no width, but they do have a length, and polygons have both a length and a width. One thing I should mention in terms of terminology, is that in this attribute table, each of these rows is called a record in the table, and each column is a field. You might as well start learning the terminology now because it's important. It's not just to make things sound more complicated, that's how we refer to these things. If you're trying to create a new column in the software, you'll have to know that as far as the software is concerned, that's a field. So, I want to create a new field. So, in the vector data model, these are our options in terms of how we can represent something. We can show things as a point. We can connect two or more points to create a line, and we can connect two or more points, or I guess three or more points with lines to create an area which we refer to as a polygon. Couple of things in terms of terminology here, one is that these are referred to as vector primitives. I was thinking why would they call them vector primitives? I think of them as the building blocks that are used in the vector data model is that's really all you have to work with. At least in the version of the data model we're working with now, there's some options and things that you can do that's a little more fancy later, but here, we'll just think of these as our options. So, these are vector primitives. One term that's important to know for these is that these are referred to as geometry. The geometry just means the things that you actually will see graphically on the map as opposed to the attribute table, which is the data that's being stored about these vector primitive objects, like a point, or line, or polygon. So, these are known as the attributes. So, we have geometry, we have attributes. These are really the two main parts that you'll normally see in a file that you're working with from a GIS point of view. You don't even actually have to have both of these. You can just have geometry without attributes. You can have attributes with the geometry. But typically, these are the two things that you'd see together. So, geometry is what you see in the map. The attributes is what you'll find in the table that's connected to the things that are being shown on that map. So, here we have a record. I mentioned that a minute ago. Here we have our fields, so just a bit of terminology to remember. So, this is an interesting question, is if we're trying to show the real world, and show it as either a discrete object or a continuous phenomenon. This is something where you can see that we have a point that's being used to represent this volcano, but very obviously, that's not really going to cut it that well. Like even if you just wanted to show, I'm no volcanologist, but I'm assuming this is the caldera. The point doesn't even represent all of the caldera, never mind all of the volcano. Just to the naked eye, if you're interpreting this, you can see that pretty easily, where does the volcano extend out to? Is it to there? Is to the shoreline? Does it actually go beneath the ocean? Which it probably does since this is Hawaii. So, there's this boundary definition question we would call it, how do you define the boundary of something to turn it into a discrete object when that's not really what it is to begin with? We're just using that as a way of convenience to show something in a simplified way that makes it easier for us to say, "Oh, yeah. There's that volcano there." By the way, there's not always a right answer to this. Sometimes, there are definitions that become conventions or accepted by an organization, or whatever happens to be a scholarly group of some kind. Other times, you'll have to make that decision for yourself. So, here we have the vector version and the raster version. This is the discrete object, version up here, so we have these individual volcanoes. Then, what's being shown here from is a satellite image, and really that's the more continuous version where we've assembled a group of squares that are the pixels that then become a photo or an image of that location. Another one we can look at is a river. If you were trying to convert this into a discrete object, how would you show this river? Where is it that you would define that boundary is being? Is the river a line, or is it an area? How are we going to generalize that? Often on a map, you'll see a river shown as just a line. So, remember that means that it actually as far as the GIS is concerned, or the data model has no width. It's just has a length. So, this blue line here is implying that there's no width to this river, which when obviously there is. But, if we were to show it as an area, and sometimes on a map, we will show it as an area. A lot of that has to do with the scale of the map as we'll talk about later. We could say, "Well, all right. So, then where do we show the boundary of this river? Is it where the water ends?" So, let's say it's along here, and I actually have this on here. So, on this particular day, that's where the boundary would be, but on another day, the water might be up there or down here. So, then, maybe you take the average of the height of the water over what period? A week? A month? A year? Several years? So, these are the questions that not to drag it out too much, but it is something you have to think about it. When you're creating a map or someone else has created a map for you, these decisions had to be made by somebody. So, in terms of generalization, how we simplify in the real world, and does that make sense? Are we losing too much detail for something? Is that enough detail? If we're going to define the boundaries of something, how do we define that boundary? Does that make sense for what we want to use it for? So, a GIS map is a collection of separate map layers that have been put together and presented in a certain way in terms of what layers are on top, and which are underneath, and how they're presented in terms of symbols, colors, map scale. I just wanted to show you here that the map that I've been showing you from Hawaii was created by Learn ArcGIS. This is actually a list of the individual map layers that they use to create this map. So, think of these as separate files that have been assembled and put together in a certain order, with certain ways of showing them to create that web map. There's the legend for that web map that I showed you before. So, each map layer contains one theme, right? So, this is the emergency shelters, that's one file. In this case, it exists on a server in the cloud that Esri is hosting, but you can depending on what you're doing, take that same data and have it on your own computer that has literally a file that you can see with Windows Explorer. So, that emergency shelters there is that layer there, so that's one theme in one file. So, points, lines, and polygons are not stored in the same map layer, and this is important. In Esri's world, they've chosen to do things this way, and there's very good reasons for that in terms of things like, data models, and topology, and things like that. We might get into later. But for now, just as a user, that's something you have to realize is that you cannot have points, lines, and polygons in the same file or in the same feature classes, we would call it. A feature classes, one kind of geographic theme for one type of thing. So, there's a couple of things here. One is points, lines, and polygons have to be stored separately, and then within that, you could have for example, different types of points together. So, you could have points that represent trees in the same file as points that represent volcanoes, but that's not really a good way of organizing your data. Yes, you could do that. So, the software won't stop you from having points that represent different types of real-world objects in the same file, but it makes it harder for you to create a map or do analysis later if you say, "Well, really, all I want to do is measure the distances to the trees, not the volcanoes." But if they're in the same file, in the same layer, then it's harder to separate those things out. So, it's a convention and a very useful one to just have all the trees in one geographic layer, one file, all of the volcanoes and another one, and so on. So, that way, you're separating things out in terms of the vector data model into points, lines, and polygons. Then within that, you're saying that one type of theme will be in this file, a different theme that's also points, for example, will be in a different file. That way, you have these different building blocks that you can mix and match as you need them. So, let's see how this actually works in ArcMap. I've opened this up. You can see that you're just getting familiar with ArcMap. This is going to be my mapping area where I'm actually going to have the map exists. This is the table of contents where we're going to have our list of layer. This is the toolbox, which we can use to perform types of analysis, and things like that on tools. Over here, is the ArcCatalog pane inside ArcMap. You can open up ArcCatalog separately, but often, it's a lot easier and more convenient to just use this ArcCatalog pane inside of ArcMap. Okay, so things I want you start to pay attention to is that, I have a geodatabase here. That little cylinder represents a geodatabase, and that means that we have a storage container in which we can then put feature classes. Each one of these, that's a feature class, that's a feature class, that's a feature class. We also have a raster dataset in here for elevation, which I'll talk about more in a different section, so if fire station roads, and vegetation underscore parks. These are from the Toronto Open Data website. Things that I want you to see here is that, so this fire stations feature class, it has a certain icon and that is four points. So, that indicates to us that's a point feature class. We have one for line feature class and one for polygon feature class. Remember, these are stored separately. So, all I have to do to make my map or to start making it, is I can select this in the ArcCatalog pane, and just drag it onto the map area. So, now we can see our fire stations on the map. We can do the same for roads, and we can do the same for vegetation.
