Before we dive deeper into InaSAFE, we will review the QGIS techniques that we covered in Unit 2. We will once more go over some of they key aspects of QGIS, including adding vector and raster layers, symbolising layers and using the Print Composer. If you feel competent in all of these areas, feel free to jump ahead to the next module, but otherwise follow along for a brief review!
As you may recall, there are two types of data that we often use in QGIS: raster and vector data. Raster data is characterised as an array of data which consists of rows and columns, like the pixels in an image. Vector data, on the other hand, consists of discrete features made of points and lines, and their position is defined by coordinates.
Let’s add vector data to a new project.
The Add vector layer dialog looks like this:
Your map canvas will now look like this:
Great! You’ve added some vector data to your map.
Remember that there are three kinds of vectors:
We have just added one layer of each type.
Raster data has different characteristics than vector data. Raster data is composed of rows and columns which form small boxes (known as pixels). The pixels contain information, which is usually expressed as greyscale or colour. The information in each pixel could be the altitude of a point, the size of the population, the area’s colour or another value.
Next we will symbolise the data to make it easier to understand.
Layer symbology is useful so that users can easily understand our maps. It is also important to make our maps more attractive. Your choice of a layer’s symbology is very important to deliver the right information.
Let’s symbolise the district layer that we’ve added:
Notice all the options that we have to change the appearance of this layer. We can change the layer’s transparency or its colour, or make even more detailed variations by clicking on Change.
We can also base the symbology on the data contained in the layer itself.
Next, let’s symbolise our roads layer.
If you use multiple symbologies (as we covered in Unit 2), your roads may end up looking like this:
The roads will then look correct:
Try editing the symbology of the POI_Sleman_OSM layer on your own.
Your map should end up looking something like this:
Your map is a medium to communicate information (as well as your ideas). Layer symbology is used to convey the content of your data so that it can be easily understood by the user. By creating a map layout, you are going a step further in using your map as a way to convey information.
For a full review of Map Composer, refer back to Unit 2. For now, let’s create a basic layout with a legend.
Your map will look similar to this:
Play around a bit with the Print Composer if you like, and refresh your memory!
Now it’s time to get back to InaSAFE!