One way you can customize your map is to modify the central meridian. That really tells the software where to center the projection for a particular part of the world. You're not actually centering the geographic mapped area itself, you're centering the projection that that map is based on. So, it's a very useful thing to be able to do, and it's actually really simple and easy to do. It customizes your maps in a way that I think is really helpful. The central meridian just tells the projection or the software how to center the projection for the particular part of the world that you're trying to map. So, that's the central meridian for these three different projections. That's all it is, it's got nothing necessarily to do with distortion or anything else, it's just a matter of, I think of it as just a way of customizing your protection for a particular part of the world. So, if you're making a map of North America, you might pick a central meridian that's at the center of the continents. So, in this case, that might be negative 100 or that would be 100 degrees west longitude, so that's west of the Prime meridian. It essentially goes down the middle of the continent. So, if I'm mapping North America, that's where I would set the central meridian to be. There are good ways to set the central meridian and not-so-good way. So, I just wanted to show you an example of where a map was made that could've done a better job of setting this up. It relates to when I first got my first iPhone and I was all excited about downloading apps. I was looking at these birds in my backyard, and I thought I'll download a bird app, so I can identify them and learn about them. So, I was fooling around with it and I saw a Cardinal. I know what a cardinal looks like but I thought I'll look it up. I looked at the range map and I went, "That's not good." I don't know if you have the same reaction to this as I do. But to me, North America looks all off-kilter, like it's going to fall over or something. I think this has to do with a central meridian. I don't know who made this map, but that's my guess. Is that, what they've probably done is made a central meridian for the eastern part of the United States. If you're just talking about the range of that part in green, that might make sense. But when you're showing all of North America, then it makes it look like it's not what we're used to seeing and it makes it look weird. If you're only showing a map of say this area, you wouldn't even notice that probably and it would be fine. But when you're showing all of North America, it just does not look right. So, I actually thought I'll try to replicate this in the GIS software, of course I would. So, this is what I think they did is they had a central meridian of about negative 75 or 75 degrees west of the Prime Meridian. So, like I said, if you were making a map of this location like that, that would be fine because that's a good thing. You're actually customizing that map, for that particular part of the world. But when you're showing a large area like this, it's just not the way people are used to seeing North America and it just looks wrong somehow. So, I would highly recommend you not do this. I downloaded the current version of the app recently, I thought I would just check to see if anything had changed, and it's a little bit better. I think they've got it almost right, it's sort of looks slightly off to me. But now, I have a feeling that that's actually done on purpose, as an artistic effect, at least I'd like to think so. It seems as though they've. I don't know if somebody there figured this out or why the design choice was made but it's just nice to see that they have a better looking map now than they did before. But on the bright side, it's a great way of illustrating a good versus a bad choice of central meridian. This is an example, the one of my students sent to me. I like it because I think what's happened here is that, this company wanted to show their range of operations around the world. It's a company that's based out of China. So, I think what they've done is they actually took a regular or a typical conventional map of the world, where the central meridian would be at the prime meridian and then they just switched it around. So, they cut it in half and the result that you get is that North America, looks like it's over here. It's distorted to one side, you can see Greenland has that effect as well and Australia you really notice that there's a distortion over here this way. So, what they should've done and would have been fairly easy for them to do is just set the Prime Meridian to be the center of the map that they wanted to focus on, which I'm assuming would be China. If you did that, then you'd end up with a map that's still the same type of projection. I'm guessing here's a compromise production, maybe the Winkel Tripel, just a guess. But that way, the map would be centered on China, would be where they want it to be and would not have this strange effect, where one, they've had to cut things in half and how these weird distortions taking place. So, just an example of how setting the central meridian, which is literally something you can do in a few seconds, would make this really nice customized version of the map, which would be great. As you can see here, I just made a quick version of a map of the world, where I set the central meridian to be China. So, now, we have what I would consider a much better version of the map, I didn't put all of the other points on it as well. But you can see the idea here is the central meridian is there and so, North America does have this distortion taking place. But with this graphic, you'll on it as well, so it's easier to visualize that. I think that's much more acceptable for people, especially in North America or whether you're used to seeing and probably Europe as well, used to seeing the central meridian being at the Prime Meridian. I don't see a lot of maps that are generated in China, necessarily, so maybe I just don't know. But I think that there wouldn't be that hard to set that Prime Meridian or sorry the central meridian to be at the center of the map, to the area that you want to do that you want to map. So, that way, you can customize that map really easily.
