The system of latitude and longitude is very old, and it's based on a sexagesimal system, which just means, a base 60 System, which is complicated when you really want to work in a decimal system, but that's the way it is. It's very old and based on this idea of degrees, minutes and seconds. So, the short form for this is DMS; degrees, minutes and seconds. As an example here, 142. This is the notation for degrees. A single quote is for minutes and double quote is for seconds. So, it's the same ideas, time, only we're using degrees instead of hours, but we still have minutes and seconds but, that's as far as it goes. I don't know if that's helpful or more confusing, but that's the notation that's used. So, one degree equals 60 minutes. One minute equals 60 seconds. So I guess, it does relate to time that way, and that's important. So, remember that. So, there's 60 seconds in a minute, 60 minutes in a degree. So, if you wanted to do the math, 60 times 60 would mean that there's 3600 seconds in a degree. Just so you know how that works. If I want to describe the location of something, here I'm in ArcGIS online, we can go to the Eiffel Tower, and see how the software will describe those coordinates to that location. Okay. So, we can use a tool within the software to do that. It's the measure tool, up here, and you can just click on a location and it will tell you what the longitude and latitude is, and so you can see that here. So, it's 2 degrees, 17 minutes, 40.34 seconds. 48 degrees, 51 minutes, 29.68 seconds. We can get a little closer look at it there, in case you couldn't see the second ago. So, that's, the DMS notation; degrees, minutes and seconds. We can also look at it, as decimal degrees. So, now we have two different ways of looking at this. We have degrees, minutes and seconds or DMS, and we have decimal degrees. They just call it degrees here but you'll notice that it's a different format or notation, for those numbers, very different than these. There are two different formats, if you want for describing the same coordinates; DMS and DD. So, why is that important? Well, the fact is, is that software, computers and people in lots of situations, would rather work with just a base ten system using decimals, than they want to work with a base 60 system. This old fashion way of doing things with degrees, minutes and seconds, just doesn't really cut it, in a digital world. So, we're much happier working with a decimal version of those same numbers. That's what the GIS software wants to use. Normally or most often I would say, when you're looking at coordinates in a table that's in a GIS format, that's the format you'll see is decimal degrees. So, you'll notice with the decimal degree format or maybe you did or didn't, there's no N for north or W for west. Computers aren't really happy to work with those either. We don't have to stick little letters on the end of our numbers. It just seems again like an old-fashioned way of doing things. So, all we do is use negative or positive signs to tell the software or to still tell someone else, where we're talking about, in relation to different parts of the world. So, thankfully at least this I find is a nice thing, is that it uses the same system of positives and negatives, as you would have in just a regular Cartesian coordinate system. In other words, in the upper right you have positive X and positive Y. In the upper left, you have negative X and they are positive Y. Positive X negative Y, and negative X negative Y. If you ever need to find a location using decimal degrees, you can at least narrow it down to a difference quadrant of the world. Different hemisphere and then north or south, based on whether they're negative or positive coordinates. If it makes it any easier to visualize, I've just flatten this out. So, this is actually using a Mercator projection. So, we've just taken the world and squished it down and flatten it. So, this might be something you're more used to seeing. One little tip to watch out for. If you ever import latitude and longitude coordinates into your software from a decimal degree format, and they end up in the wrong part of the world. So, there in Australia, when you wanted them to be in North America or something like that. The first thing I would look for is, are they missing the correct sign. So, did the negative sign gets stripped off by some method or somehow, or is it a positive instead of negative, and so what that'll do, is that the software will just read those numbers in decimal degrees, look for the positive or negatives and assign it to the part of the world that it thinks it belongs in. For whatever reason it happens more often than you might think, that these symbols, the signs can get screwed up or are missing or that thing. So, just always remember that and check for that. If something's not mapping correctly. Things look correct relative to one another, so all of the dots are in the right location but they've all been shifted. It could be because of the sign. Here's a little trick or tip that I find interesting in ArcGIS online, is that if we have the Eiffel tower here and we have the decimal degree format, for longitude and latitude. You can specify in the URL for the web browser, where in the world that it should be focused on, based on the coordinates that you give it. So, if you use that URL, it'll just load a map of the world, but if you add to that URL this little extra part here. So, that's just the notation that's used by the app. You're telling it, to center the map on these coordinates and so when you do that, and you type that in, it will actually center it on the Eiffel tower. Not only that, but you can have it center it and also set the zoom level. So, you can zoom in or out to a specific amount and so, if you add this last part here with the n level equals eight, that will set the zoom level to the desired amount. So, the idea is that, you can send somebody that URL, and specify exactly where in the world they will see that map at and at this scale that you intended. That's a fun thing to be able to do. You can also add this last little bit on the end. The end map only equals true, if you want to get rid of that little side pane. So, I'll show you that without it, adding that little notation at the end, which is fine. It's not that it really bothers me but sometimes, I like to have the map take up the whole screen. So, if you add that last little bit and map only equals true, then it takes out that map pane and you've got the map filling the entire screen.
