Vector data is arguably the most common kind of data you will find in the daily use of GIS. It describes geographic data in terms of points, that may be connected into lines and polygons. Every object in a vector dataset is called a feature, and is associated with data that describes that feature. The goal for this lesson: To learn about the structure of vector data, and how to load vector datasets into a map. It’s important to know that the data you will be working with does not only represent where objects are in space, but also tells you what those objects are. From the previous exercise, you should have the roads layer loaded in your map. What you can see right now is merely the position of the roads. It will show you a table with more data about the roads layer. This extra data is called attribute data. The lines that you can see on your map represent where the roads go, this is the spatial data. Vector data represents features in terms of points, lines and polygons on a coordinate plane. It is usually used to store discrete features, like roads and city blocks. The Shapefile is a specific file format that allows you to store GIS data in an associated group of files. Each layer consists of several files with the same name, but different file types. Shapefiles are easy to send back and forth, and most GIS software can read them. Refer back to the introductory exercise in the previous section for instructions on how to add vector layers. Databases allow you to store a large volume of associated data in one file. You may already be familiar with a database management system (DBMS) such as Microsoft Access. GIS applications can also make use of databases. GIS-specific DBMSes (such as PostGIS) have extra functions, because they need to handle spatial data. You will now see the first dialog again. Notice that the dropdown select above the three buttons now reads “land_use.db@…”, followed by the path of the database file on your computer. The layers in your Layers list are drawn on the map in a certain order. The layer at the bottom of the list is drawn first, and the layer at the top is drawn last. By changing the order that they are shown on the list, you can change the order they are drawn in. The order in which the layers have been loaded into the map is probably not logical at this stage. It’s possible that the road layer is completely hidden because other layers are on top of it. You’ll see that the map now makes more sense visually, with roads and buildings appearing above the land use regions. Using the random palette automatically assigned when loading the layers, your current map is probably not easy to read. It would be preferable to assign your own choice of colors and symbols. This is what you’ll learn to do in the next lesson. Source.