[MUSIC] Hello everyone and welcome back. In this lesson, I'm going to demonstrate how we use scale in GIS. You'll learn what scale is and what it means for data quality and for your maps. You'll also learn about how to talk about scale so that you can communicate with others about the scale of your information. So to begin with, we've talked about scale in passing in some of these other lectures but what is it really? Simply put, the scale of a map or data describes the size of that map or data on your screen or on a sheet of paper relative to the size it is in the real world. So up in the top here I can see my map scale and that it's one to one million. And what that means is that one unit on my screen equals to one million units in the real world. And we commonly use inches, so that would be one inch on my screen is one million inches in the real world. Now, since I'm familiar with this data in this area, I know that it makes sense that this data is at one to a million scale right now. But since you're probably not as familiar with this area and this data, it may not make as much sense to you that that's the current scale, at least not intuitively. So let's verify that scale by using the measure tool. Click on it to bring it up. And I'm going to click on some spot that looks like it's about an inch on my screen here. And if we do this, that's approximately one inch on my screen. And I'll see that 23.14 kilometers there. Now, I could do all the math to see if one inch at one to a million scale equals 23.14 kilometers, or I can make Google do that work for me. So if I bring up a web browser and go to Google, I can type in one million inches in kilometers, which you see I've done before, and it says that's 25.4 kilometers. So, we were a little off but pretty close and we could see that one inch here at one to a million scale, one million inches, equals about 25 kilometers, and that's how our scale is represented here. So one important thing about scale is it matters with respect to the detail of our data both with how much detail is displayed but also how we record detail into our data. So if we look at this big lake in the middle here at this scale we can see that it's a little bumpy here but there's not a lot of detail in this shoreline and this outlet over here. But if I zoom in to the lake, all of a sudden we get much more refined detail. And you could see a lot more about what's going on, even though there are still spots that we can't see the detail of. And as you can see, we've increased our scale by about five times. We went from one over one million to one over about 200,000 here. We can do this again, zooming into this bottom corner where the detail is missing, and get much more detail and start to see that there's actually a little island in here that we couldn't see at that previous extent. So scale matters definitely for how we view our data. Imagine on the digitizing side though, when someone's creating these features. If they're doing it by hand, which you'll learn how to do later in this course, that if we were zoomed way out here At the one to a million scale, they couldn't possibly digitize with that level of detail. So that's another use case for scale. We often talk about features that we've digitized at the scale that they were digitized at. So we might say, we might fix our scale when digitizing to one to 60,000 here and say that these features are only valid down to that level because if we digitize them here, when we click on different points, the accuracy that comes into the data is dependent on what scale we resume to. Just think about trying to create these little islands here, while zoomed out even further, that if I was to try and click on the spot on the map that those islands were in clean outline of them, I'd get a lot of noise. I'd miss. So they're not valid zoomed further in than the features were created at. I want to point out two things that just happened when we zoomed in and out. Number one is if I zoom in using the zoom tools, the scale in the top here automatically gets updated. Any time I change the extent so we're not one to 22,000. Any time I change the extent that gets updated. So if I go back to the previous extent, it automatically updates the map scale for me up here and we go to the correct extent here. Likewise, just a moment ago you saw me type in a scale here. If I want to go to a specific scale, like one to a million again, I can type it in there. It will take me to that scale. Now, I've been talking about scale as this unit less thing or when it has units it's the same unit like inches on both sides of this equation. But in certain professions I've heard forestry, that sometimes it has different units on each side of the equation. So it might be inches on one side and feet on the other, which would affect the math and affect what size on your screen equals to what size on the ground. You should just pay to what other people are talking about in your profession and make sure that you're using a scale the way everyone else is. Most professions use scale the way I've described so far, but a few use different units on each side, so watch out for that. One other terminology thing that's pretty important is the difference between large scale and small scale. This trips lot of us up, myself included, and when I see a number like this, I always want to think it's a large scale because the number one millions in it and that maybe that one to 60,000 that we resumed into before that this is small scale. That's wrong. And there's a really easy way to remember, that this here is large scale and zoomed out is small scale. And the way to remember it is to think of this as a fraction. If we replace this colon in our minds with a division operator and think of it as one over 60,000, one over 60,000 is bigger number than one over one million. So this bigger number here is large scale and this is a large scale map relative to the one to one million, which is a small scale map. Sometimes in an exchange with someone else, you might ask for a large or a small scale map and that's where this kind of thing matters. Another place that talking about scale can matter is when working with pre-made maps from groups like USGS. People will talk about one to 24,000 topographic maps, which describe the detail level of the map that you are looking at and, oftentimes, the area covered because at that higher detail, a smaller area fits on the same map. So if you ask for one to 24,000 map, you're asking for a higher detail map of an area. The last functional thing I want to point out in this lecture is scale dependent rendering. We've talked about this before but if you go to the layer properties, and go the general tab, you can specify for a layer to not show when you're zoomed out beyond a certain scale or zoomed in beyond a certain scale. So, if I say maybe I only want this layer to show up when we're zoomed in so as not to clutter up the map when we're zoomed out. Maybe we have more important features to show when we're zoomed out. I can say maybe don't show this one zoomed out beyond one to 100,000, and I'll click OK. And right now, we're at one to 60,000, so we're zoomed in far enough that we can see it. But if I keep zooming out and showing you the scale there as I zoom out, I don't see the layer anymore. But if I zoom in, we're under 125,000, I still don't see it, we're under 100,000, I just now see it. This is a useful cartographic tool for creating one map document that helps you view your data but also maybe helps you export maps at different scales. You can set up one map document with symbology with many layers that are common, so that they all show up across scales, but maybe you do an overview map where certain layers don't show up. And then you zoom in to different areas, like with data driven pages, and show these other layers that show up when you're zoomed in. That's just one use case. And finally, remember also that scale is represented on maps we make using the scale bar that we inserted in the last class, or you can insert the scale text that we've been working with in this lecture onto your map directly as well. Okay, that's is for this lecture. In this lecture you learned how to use different scale tools in ArcGIS from setting your scale in this box here, or scale dependent rendering, and you also learned about how to talk about scale from large scale to small scale and how scale is a factor in creating data and in viewing data. See you next time.