A common procedure when you're preparing data for a project is that you will need to merge datasets. So this is a common situation, where you have two datasets that are different feature classes. Often, this will happen with really large datasets. For example, these are topographic datasets from the government of Canada, and they have them for the entire country. And so a strategy the data providers will use is to cut up the data into tiles, so this would be one tile or map sheet, this is another tile or map sheet, in order to distribute it. It just makes for smaller, more manageable files. But inevitably, when you're putting the data together for your project, you may want to put those back together again in order to treat them as one file, one feature class for your project. It's some kind of GIS Murphy' law, I think, that if you're trying to map an area, it'll always end up kind of overlapping between two study areas or actually, even worse, between four or more. And so this is just a very quick explanation of how you can merge those data sets into one new feature class, and then you don't have to worry about boundaries or so on, so let's have a look. In our toolbox, under the general toolbox, there's a merge tool here. So that's what I'm looking at in the dialog box here. And all I'm doing, in this case, is specifying two feature classes that have these kind of, these are names that the government of Canada gave them, so they're not the most user friendly, but those are map sheets, 107B, 02, and so on. And all I'm going to do is merge those two together and create one new feature dataset called merge_water. And in this case, I'm going to store it as a shape file, and that's why it has the SHP extension. Great, so now I've got one new feature class. This is a new dataset that I've got all the water data into one new feature class. So everything's great. You can see that the common attributes have been carried over. So these are the attributes from the input. And you'll notice that all the field headings are the same in both. And so these are from the original map sheets, and this is from the merged version of that. So it's carried over all of the attribute data from both datasets. However, if we zoom in here a little bit, you'll notice that there's actually lines in the middle of this lake, in the middle of this lake, in the middle of this lake. Hmm, that's not ideal. I've actually been to this lake before, this is Campbell Lake here. It's in the Northwest Territories, really nice spot to go fishing if you ever have the chance, or swimming. And I can tell you for a fact that there is no causeway there, no bridge there, no reason, really, for that line to be there. So why is there lines in the middle of this lake? What's going on? Well, if we look at the original map tiles, you'll see that this lake actually spans two different map sheets, okay? And so when it happens there, if I just go back to here, is that this is on, let's call this map sheet 1, this is on map sheet 2. And if you've created data or you know about digitizing, how that works is that the person that was digitizing this lake would have been clicking here, and clicking here, and clicking here. And so they would have been essentially tracing the outline of this lake. But when they got to the edge of the map sheet, so they were digitizing off of the paper map sheets that were created as a map series long ago, they would have gotten to the edge of that sheet of paper. And they would have just gone across there and started digitizing back down this way. And the same thing with this one. They would have digitized the edge of the sheet of paper, gone across, and gone back up that way. And so that's literally how those digital datasets were built, were from these paper map sheets. And so that's been carried over into my result. Even though I merged them together, it doesn't know to do anything with that. It's just said well that's the way it was, so I merged them, and that's all you get. So what could I do to get rid of those lines, hm? What would be a tool that would allow me to somehow dissolve those lines? Yes, the dissolve tool, absolutely. Let's try that. Here's our dissolve tool. All we have to do is find any attribute where all of the lakes in both of those datasets have the same value. It doesn't matter what the value is. Remember, the dissolve tool is based on the idea that it's checking all of the polygons to say, are they sharing a boundary and do they have the same value? And if they do, it will dissolve them. So I just happen to know that the code here is the same for all of them, so I can use that to base the dissolve on. So this is before the dissolve. And this is after the dissolve. That's all there is to it. You don't always have to do a dissolve after you merge them together. But it's the kind of the thing you want to check for to make sure that it's doing things the way you want. For example, if you were calculating the area of each of the water bodies, if you hadn't done a dissolve, then this would be calculated as one area, and this would be calculated as another area. You would get erroneous results. So you want to make sure that you check for things like that and perform a dissolve, if it's necessary. And so then you've got your merged datasets. You've taken care of any of these kind of spurious, erroneous boundaries, and you can work with your data to your heart's content.
