[MUSIC] Hello everyone and welcome back. In this lesson, I'm going to go over the dissolve tool. In this second class, we did a little bit with the dissolve tool when we talked about percent overlap, but we'll go over it in a little more depth here. In the process we're going to go through multi and single part features and talk a little bit about what those are as well. So to begin with, what are we looking at? We're looking at counties in the contiguous United States. With a data set like this, I could do a lot of different things, but maybe I would like to use data at the state level. Now, I could get state level data from the same place I got this data, from the United States census bureau. But maybe I have other data that's at a specific unit, and I want to aggregate It up to a different level instead, this is what the dissolve tool does. It basically dissolves the boundaries between features that we specify so that we get features that are larger and combine multiple existing features in our dataset into one. So lets take a look. Now we been used to going through analysis tools, but in this case we're going to go to data management tools, and in the generalization tool set, we have dissolve. And, it's generalization because dissolving is basically generalizing our polygons to a larger unit. Again, as an illustration of what we're doing here, we take inputs that have these particular boundaries between and we get an output that no longer has those boundaries. So let's put our counties as our input feature and I'll call this states from counties. And if I don't provide a dissolve field it will dissolve all to one feature, so let's just do that really quickly and ignore the rest of these features for a second. I'm going to create multipart features, I will need to do that for this, and then I'll click OK, and let's see what we get out of that. Again, running in the bottom right hand corner, just like all our geo-processing tools. While that's running, let's set up our next dissolve as well. So, we'll take a look at that in a moment but then let's do this for now. So, I'll do dissolve again, and once again let's make counties our input features, and I'll call it counties from, or states from counties layer, since I misnamed the other one at this point. And in this case, we're going to select a field. And I'm going to select the state geo ID field which provides an ID for which state a county is in. And then I can also provide a statistics field which will do kind of what we got with spatial join where we can have it. Take the attributes of all these features it's combining and make a new attribute out of it. So let's say we want the area water field, we can do a statistic type of sum it up, because we want to know given all of these counties that have an area that's from water, we would like to add that up to get the new attribute. And we'll do the same thing with the area land field and we'll sum that up as well. And now down here at the bottom where it says create multi part features, we can check or uncheck the box. If we remember from when we barely explained it before, a multi part feature is a feature record in our attribute table that is associated with multiple polygons. It comes up as one geometry, there's still just one record in the attribute table, but there may be many polygons that are apart of it, and we'll look at that in just a second. A single part feature means that for each polygon we have an attribute record, even if we're duplicating some data. They each have different uses, maybe for the state of California we want one polygon eventhough California has some islands. But maybe for other locations we would like to have those islands be separate polygons. Maybe if we're doing place names instead, we would like separate records for each of those islands. Let's create multi-part features again, and I'll click OK and that'll run. And while that's running let's explore what happened when we ran without providing an attribute here. So we didn't provide an attribute to dissolve on, so it just dissolved all of the feature boundaries, and if I right click on it. Let's just rename it just so we don't get confused, I'll just call it USA. And if I open the actuary table, I have one record because I created multiple features, but notice Puerto Rico over here is part of that same polygon. So we have a multipart feature that encompasses all of the US as well as Puerto Rico. And, if we zoom out, we can see Alaska, and Hawaii, and all the other islands affiliated with the United States. Again, because we didn't choose a dissolve field, and because we chose to create multi part features, that came in as just one single polygon feature. But, when we select it as a dissolve field here, we dissolved on an ID for each state, and instead we got the state boundaries. And it kept the boundaries between each state, because the counties in Nevada and the counties in California site didn't share that attribute, they had different values for the county ID attribute or the state ID attribute. So they didn't break the boundaries between those 2 states, and instead left the county boundaries in between there in tact, but within Nevada, the counties shared that attribute value and so it dissolved those boundaries. Now those of you familiar with the United States may have caught a relatively glaring error here but its not in an area I been making a look at, its over here with Michigan. And it just have to do with, what happen when you dissolve this upon other futures, you need to make sure that those futures actually represent the things you are tying to get, a function to get accurate state boundary here, am not exactly getting a perfect boundary with Michigan, it's including some other areas, probably parts of the great lakes, that i was not expecting to happen. So you'll want to watch out for things like that when you're dissolving features. Pay attention to the source data you're dissolving from and what you're trying to get out of it, and make sure there's a direct translation between the two. Okay, that's it for this lecture. In this lecture I showed you the dissolve tool, and we talked about what happens when you select an attribute to dissolve on versus when you don't select one. And then we also discussed multi part and single part features. Okay, see you next time.
