3. Vector Data in Action, GIS kurs, GIS Data Formats, Design, and Quality, W1 Course Overview & Data Models and Formats, Lesson 1 Vector and Raster Concepts

3. Vector Data in Action

3. Vector Data in Action, GIS kurs, GIS Data Formats, Design, and Quality, W1 Course Overview & Data Models and Formats, ...

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[MUSIC] Hello everyone, and welcome back. In this lesson, I'm going to show youa few more vector data concepts by really emphasizing how vector data is builton the concept of point locations and connecting them with edges. So, to begin with, we're just going tozoom in on Lake Malawi down here in the eastern corner of Africa,and I'll use a bookmark. And I'm going to createsome features right now. Now I'm not going to show you allthe details of how to create features. We'll do that later in this class. So if you really want to know andfollow along, just wait til later in this class andthere will be a lecture on how to do that. For now, we're just focusing onhow vector data is structured. So first,we can represent lakes as a point, we just generalize them allthe way down to a point. And I can put down a point and call it Lake Malawi,and we have our point. And on the map there,we can label that point so that it shows up andwe have that representation. So if I make it nice and big,we can see Lake Malawi here. So we can represent vectordata as just a point, and we can get that point's latitude andlongitude if we want to into fields. But we know that that pointhas a set of coordinates, so that's how we place it on the map. Now, that part might seem obvious,there are points, but if we zoom down here to the Shire River,I'm going to zoom in even a little closer. We can also make lines, and these too are basically built outof points, these point locations. So if I switch to this line featureclass I'm going to edit this line here. I click and I see a point on the map. And then as I move my mouse aroundit's trying to make a line that fits there for me. So I can create another point here,and it just puts an edge, a line, in between those two points I made. And it's fitting the line to matchmy points that I'm putting down. So every time I click, it's creatinga point and that most recent point is red. That's the point that's active andit's trying to connect to. And I click again and it moves along, and it cements that previouspoint in the green there. And I can keep going,creating this line out of points. So, once again,we're generalizing this river. We're taking thisthree-dimensional thing and basically making it nearly onedimensional, but kind of two dimensional here, and turning it into this narrowline that curves through its area. And that line is completely constructedout of points, and ArcGIS does that work of connecting the points, wherever I placethem, with edges or lines in between them. So really foundationally,we're coming down to the vector feature information beingbuilt out of these point locations. Even though,when I finish this feature here, it becomes just a line likeanything else we've seen. We can see, as we just did that,it's actually built by point locations. Now, polygons are the same. So if we go back to seeing Lake Malawi andI switch to digitizing that, I'll turn off that point feature, andI can start digitizing the polygon. And again,we see that same concept of that red dot. And I can move around, and it's trying tomake a line that connects my cursor to the most recent point I laid down. But once I click that second feature,it then has two lines. It's trying to fill an area for me. And when I click that third one,it starts showing me the polygon's current filled area in the color ofthe polygon in the layers symbology. And soI can kind of click through all this, really quickly digitizing the lake here. I'm going to be very sloppy,but again, I'm going to show how to do this all later in this class andyou'll get lots of practice with it. And you'll be very sick of it atsome point, because digitizing is what a lot of new GIS peoplespend a lot of their time doing. So now I have this polygon and I just created it again with thisclicking around the boundary. And we have all these points that actuallydefine the locations of this polygon and then it connects those points with edges,and then it fills the area for us. And the actual information that we'reproviding is this string of coordinates, these point locations. But we are now saying that, as a datastructure, we infer information about everything that's inside of this area,that's what making a polygon does for us. So I can again finish this,and I got a polygon. And just like before, I can open up the attribute table andI can give it some information in here. I can say that this is also Lake Malawiand, Make that a little more visible. And what I want you to get reminded ofhere is that each feature class has many features in it, and those features aredefined in the way that we just described. But that each feature also has anindividual record and that, in fact, this feature information here, this polygon,is just one field in this attribute table. It's just one bit ofinformation about the polygon. The rest of it is thistabular information, this attribute informationin this individual's record. But the polygon we created is storedeffectively in this shape field, and then the rest of the informationis in other fields. And we have this single object here. Now, the point is also an object model. It's just that the feature informationthat we have happens to be a point instead, and same with the line. But they all have an attribute record,and you can think of it as the feature having an attribute record oras being a member of the attribute record. Either way,whichever's most convenient for you, but know that both are kind of true. Okay, so that's it forthis lecture, it's very brief. I just wanted to demonstrate to you thevector data model and its basic concepts, which are that we build everythingbased on these x and y point locations. We set down the coordinates on the map andthen we do things with them. Sometimes we just leave them aloneas a point and have attributes, and other times, we say, okay, connect thispoint to this other point in a line. Or connect these points together andfill the area and create a polygon for me, and we'll generalize informationinside of that area in one object. So I hope that that helps you visuallyunderstand how the vector data model works a little more, and that you'll take that with you as you go into the restof the class, as we create more data. Okay, see you next time. [ Pobierz całość w formacie PDF ]

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