Video: Creating buffersIf you've ever seen a map of an earthquake you might recall seeing rings around the quake's epicenter, showing how far away the tremors were felt. Those rings were the result of a buffer analysis. Creating buffers around elements on your map is a very common geoprocessing task that is useful for a wide variety of analysis and display purposes. Basically a buffer identifies regions that are within a certain distance of any point, line, or polygon feature that's in your map. The buffer tool creates new polygons that surround the identified features, and there are a couple of different tools in the arc toolbox, that'll help create them.
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If you've ever seen a map of an earthquake you might recall seeing rings around the quake's epicenter, showing how far away the tremors were felt. Those rings were the result of a buffer analysis. Creating buffers around elements on your map is a very common geoprocessing task that is useful for a wide variety of analysis and display purposes. Basically a buffer identifies regions that are within a certain distance of any point, line, or polygon feature that's in your map. The buffer tool creates new polygons that surround the identified features, and there are a couple of different tools in the arc toolbox, that'll help create them.
Now if you're toolbox isn't open. Go ahead and open up the Arc toolbox here. So we're going to use our map of dairy locations within Washington state and precisely identify what areas are near the farms. I'm going to go into the analysis tools here, into proximity, and I'm going to choose this buffer tool. The buffer tool requires some input features. Those are going to be our dairy points, so drag, and drop them into input features. The output feature class is where we're going to save this, so let's go ahead and press browse here. I'm going to come into my working folder here within the data files folder.
We'll create a new geo database, and I'm going to call this buffer. I'll double click to go inside of the buffer geo database, and here we're going to call this dairy rings. Go ahead and say Save, and now we can tell it how far out we want the rings to be. In this case I want to see all the areas that are within 20 miles of a farm. So I'm going to choose the linear unit of 20, and change this drop down list here, to miles. All of the other fields can be left the way they are so go ahead and just say okay. So when it gets done we can see all of the areas that are within 20 miles of a dairy farm. Maybe this area will help us identify sites where we need to focus soil or water monitoring efforts to ensure that the dairy operations aren't adversely impacting the local environment.
The buffer technique can also help us locate the best sites for a new farm supply store or feed silos. But buffers don't have to just be used for analysis work. They can also be used to achieve certain cartographic effects. One way that I've seen them used is to create what are called water vignettes that you might have seen on an old style nautical chart. For this we'll use a built-in script that will run the buffer tool multiple times. It's also found in the toolbox under proximity, and it's this one here this multiple ring buffer. The multiple ring buffer tool can be a bit processor intensive and it might take a while to run.
So lets just do a sample run on a few islands in San Juan county. I'm going to go ahead and turn off my dairy rings and also the dairy points here. I'm going to go to my bookmarks and choose San Juan County to zoom into the islands that we're interested in here. I'll start by using the polygon selection tool here, to select just a few islands in the county. Now it doesnt matter if you select exactly the same islands as I am. If you grab a few extra, or leave some out, that'll be just fine. The goal here is just to limit the features the tool's about to run on, so that it speeds up processing time. I've gone ahead and selected a few of the islands, and I actually selected one of the counties as well.
So I'm going to choose The feature selection tool, back to the rectangle and I'm going to shift click to deselect the county boundary here and also over here as well. Now that I have some islands selected I'll right click on the Washington shape layer going down to selection and choose create layer from selected features. That'll add just those islands to the map by themselves. And I can go ahead and turn off the rest of Washington here. So now I have just a few islands to run the multiple ring buffer tool against. I'll double click on multiple ring buffer to start the tool. And I'm going to go ahead and take this Washington selection, those are just the islands and drag those into the input features.
The output feature class, I'll click on the browse button, in my buffer geodatabase that I created. I'm going to call this water vignette. Go ahead and say Save and now we're going to specify how far out we want the rings to occur. I'm going to put in the first one at 500 feet and press the plus button and that'll add it to a list here. The next one is going to be 500 feet further out so it'll be at 1,000 feet. Go ahead and say plus, the next one will be 1,000 feet out from that so that'll put it at 2,000 feet. I'll press plus. The next one is 1500 feet further. So it'll be at 3500 feet.
I'll press plus. And then finally, we'll have one 2000 feet further out from that, which will put us at 5500 feet. Go ahead, press plus again. I'm going to scroll down the list a little bit. And make sure that the buffer either says default, or change it to feet, which is the default units for this particular map. We'll go ahead and say okay to run the tool. The multiple ring buffer tool will take just a moment to run. When it finishes, we'll get the symbology of all these different polygons that are around our islands. Let's go ahead and drag this selection on top of the water vignette layer. And now we'll go ahead and symbolize the water vignettes.
I'll double click on it to open the Property sheet. And in Symbology, I'm going to click on this header here and choose Properties for All Symbols. Here I can choose this hollow property to make them with no fill. And I'll change the outline color to a bright blue color, here. Let's go ahead and say okay. Apply. And I'll say okay again. And so now you can see we have multiple ring buffers around our islands, which highlight this kind of water effect. So that's how the buffer tool works. The buffer geoprocessing tools offer another easy way to create additional geometries in your maps that can aid further analysis efforts or just create that finishing cartographic touch.
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