Using Vector Data Effectively

In the previous chapter, we learned how vector data compares to raster data. Although every feature can only represent one coherent entity, it is a way more powerful and flexible data model. With vectors, we can store a tremendous amount of attributes linked to an arbitrary number of features. There are some limitations but only with some data exchange formats. By using spatial databases, our limitations are completely gone. If you've worked on a study area with rich data, you might have already observed that QGIS has a hard time rendering the four vector layers for their entire extent. As we can store (and often use) much more data than we need for our workflow, we must be able to select our features of interest.

Sometimes, the problem is the complete opposite--we don't have enough data. We have features which lack just the attributes we need to accomplish our work. However, we can find other datasets with the required information, possibly in a less useful format. In those cases, we need to be able to join the attributes of the two layers, giving the correct attributes to the correct geometry types.

In this chapter, we will cover the following topics:

• Querying and filtering vector layers
• Modifying the attribute table
• Joining attributes