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The third georelational model offered by Esri, is the Geodatabase model and it was introduced in ArcView 8 or ArcGIS 8. Unlike the Georelational model, the Geodatabase model is a contained file system, and is a true relational database with all the advantages associated with database management. Instead of a flat file system the Geodatabase stores the Geo graph data as objects and you can apply structured query language, or SQL, functions and operators on the Geodatabase.
Esri's first model started with the personal geodatabase. Which was based on the Microsoft axis database. And has a two gigabyte storage limit. It is being phased out currently. And in place, a new file geodatabase with no size limit is available. Which is important for GIS data, because it often exceeds the two gigabyte limit. The geodatabase vocabulary is simple. Geodatabases have two main aspects, feature datasets and feature classes. Feature datasets house a series of Feature Classes that share the same geographical projection.
I'll cover projections later in this course. However, there can also be stand alone feature classes that do not share the same projection. There is no limit to the number of feature classes you can have within a geodatabase, as a stand alone, or within a feature dataset. You can even put raster data within a geodatabase, and we'll cover that later when we discuss the raster data model. Now let's look at the geodatabase in ArcMap. Again, I'll start with a fresh document. In the example folder, you'll find the geodatabase that I've created for our video.
Let's grab that now. When we open up our catalog and navigate to that geodatabase, you will see that it's called landuse_Ontario geodatabase. And within there we have one feature class. Landuse_polygons. If we look at this geodatabase, within the Windows environment, we'll see that it has several files associated with it, but they're all under one particular folder. Let's do that now. Here we are in the exercise file example folder. Notice landuse_Ontario.gdb.
The geodatabase we're dealing with is present, if we double click on the folder, we see a bunch of files associated with this geodatabase. The geodatabase structure makes it very easy to share data. All we have to do is simply grab this folder or zip this folder, and give it to a friend and they will have everything that's contained within the geodatabase. Now let's look at the details in ArcMap of this particular geodatabase. Here in ArcMap, I'm going to add the one feature class that's associated with our geodatabase. Double clicking on the land use Ontario geodatabase, you can see the one feature class I have, land use polygons.
Let's add that. Later in the course, I will show you how to create a geodatabase and set it up with feature datasets and feature classes. Now, let's take a look at the attribute table associated with this layer. There are two things that I want you to see. First is this shape column. This is where all of the data is stored geometrically. And so, when you see polygon listed here, polygon is actually an object that's embedded within this row. Also, when we have a geodatabase created, if it's a polygon layer, shape length, and shape area are added as columns in the data.
The units here are associated with the geographic units, related to the projection. In this case, they really are meaningless to us, because this file is a simple geographic coordinate file for latitude and longitude. If we re-projected this with a projection in English or metric units the results would be meaningful. I've already done this, so let's take a look at that. Here I'll close the table for ease of our visualization, and now I'll open up our catalog, and that particular projected layer from the exercise files.
Now, with the same feature class added to the Table of Contents, we can right-click, and choose the Attribute Table, or open up the Attribute Table, and you can see here Shape Length and Shape Area have different numbers. Let's open up this one and see that very difference. There they are. This one is the projected, in this particular case, it's a UTM projection. So, we have meters represented here for shape length, and shape area. Whereas land use polygons only has the latitude and longitude shape lengths, and shape areas, which are meaningless to us.
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