This brings us to our next section, which is all about maps. Of course, maps are one of the most common uses of geospatial data. So first, let's talk about what is a map? A map is simply a visual representation of geographic information. There are several different types of maps, some of which you may be familiar with and some of which you may not.

The first type of map is a general reference map, which is probably what comes to mind when you first think about maps. These include street maps such as Google maps or paper roadmaps for those of you old enough to remember those, tourist maps, and political maps.

So if you remember the map of the United States or of the world showing geographic borders that were hanging in your elementary school classrooms, those are all political maps.

Topographic maps are detailed elevation maps which show contour lines to mark different elevations. So if you're looking at a map of say the Rocky Mountains, with the contours and the elevation, that would be a topographic map.

Thematic maps are maps that include information beyond geographic features. So a weather map would be considered a thematic map, as would a geology map. A map that shows animal habitats would also be considered a thematic map.

Navigational charts are the sorts of things the pilots and sailors use to navigate and figure out where they are and where they're going. And then finally, there's cadastral maps, which are maps that show land parcels and are used for real estate sales, land surveys, and valuations.

To make this all a little more concrete, and to illustrate the various types of maps and how they look, let's look at a few examples. So this first example is a general reference map of the Grand Canyon National Park. So you can see the path of the Colorado River here. You also see local highways, and you can see the geographic borders between Arizona, Utah, and Nevada. So this is kind of what you think of when you think of map, it's generally what you have in your head is the general reference map.

The next example map is a topographic map showing Colorado. So you can see Denver and Colorado Springs labeled on the map, and the contour lines and shading on this illustration represent the elevation. This is an example of a thematic map, and it's showing the seismic hazard for the United States from the USGS. The different colors are indicating the level of seismicity. So the darker the color, the more seismic the area. So the purples and reds are very highly seismic areas and white are non-seismic, so no seismic activity at all. And then the blues and the greens are low seismicity, so you're not in huge risk for earthquakes in those areas, but they're theoretically possible.

Finally, this last example is a navigational chart of the New York waterways, and you can see this is showing the Hudson River and the East River. And it looks very different from the other maps because it's really designed for a very specific purpose, which is for sailors to navigate through these waterways.

You may have noticed that each of these example maps are two-dimensional. But the thing about the earth is, that it's a three-dimensional surface. We live on a 3D planet, but maps are flat, except for globes, of course. So how do we represent a 3D planet on a 2D surface? The answer is map projections. This means we can project a three-dimensional image onto a two-dimensional surface. And there's a number of ways to do these map projections.

Before we start talking about map projection specifically, let's do a little exercise to help you understand the concept of projections. All you need for this exercise is a piece of paper and two pencils. Take one of the pencils and hold it so that its shadow falls on the piece of paper. Now use your other pencil to trace the shape of the shadow. We now have projected a three-dimensional object, the first pencil, onto a two-dimensional surface, the paper, as a shape or line, depending on how you did your traces.

Okay, so now we're ready to talk about some types of map projections and show some examples. A very common one is the Mercator projection, which is a simple cylindrical projection where you take the globe and you project it onto a cylinder, just like we projected our pencil onto the piece of paper. And then you take that cylinder and you roll it out flat, and that's how you get your flat two-dimensional.

Another type of projection is a conic projection. In this case, the three-dimensional globe is projected onto a cone, and then the cone is rolled out flat. This example here is the Lambert conic projection, and you can see it looks quite different from the Mercator projection. You can actually see the outline of the cone in the flat projection.

This next example is an azimuthal equidistant projection. There's a center point for this map. It looks like somewhere in California, with all points on the map at the correct proportional distance from that center point. In addition, the direction or azimuth from the center point is correct for all points, and that's where this projection gets its name.

The last type of projection we're going to discuss is called a pseudocylindrical equal area projection. I remember seeing this type of map back in elementary school. As the name suggests, this projection preserves the area of map features such as landmasses, but at the price of distortion of shapes and distances.

Now, these four types of projections are by no means the only types of projections that you can do for a 3D globe onto a 2D map. But hopefully, this gives you a flavor of how you would do those map projections.