Symbolising data
We'll get straight on here with symbolising some of your data to make it look much nicer and easier to interpret meaning from. A bright green Antarctica is not what people expect to see on their maps! This page will only cover symbolising vector data, we will cover rasters later on if time allows.
Exercise
Polygons
Symbology options are located within the properties of each layer.
To access these, either double click on the layer, or right click and select properties. Do this with the coastline dataset to start with.
Once the properties are open, you should be able to see various tabs on the left-hand side. There are very many useful tabs here, and far too many to discuss in this course.
2. For now, we want the Symbology tab, so click on this.
3. To change the colour of the polygon fill, select the little drop down arrow next to your colour (highlighted by the red circle below) and pick a more suitable colour. A white or very light grey is often used for Antarctica. Click 'Apply' at the bottom of this page and see how your changes look.
Your change should hopefully improve the appearance of Antarctica, but do you think it would look better to have the ice shelves a different colour to the land? Let's do that.
4. Open the Symbology tab back up if you closed it. Along the top, you can see that our polygons are currently shown as a 'single symbol'. We want to show them as 'categorized' - click on the 'Single symbol' button and change it to 'Categorized'. The main part of the panel should now be blank.
5. This shapefile contains attributes defining whether each polygon is land, ice shelf, ice rumple or ice tongue. This information is contained in a field called 'surface', so we need to tell QGIS that we want to use this field called value to define our symbology.
6. In the 'Value' drop down just below the word 'Categorized', click the drop down arrow and select 'surface'
7. Next, click the 'Classify' button, near the bottom of your symbology pane. This gives each of the surface attributes a random colour. These colours are generally not very nice. Some automatic colour ramps are available in QGIS - have a quick play around with these by selecting the drop down where it says random colours.
8. You are unlikely to find a nice colour ramp for this use here, but if you had data that needed a nice, typical colour ramp, then these can be very useful.
9. We will manually assign each of the values a specific colour. Click on 'land' and then click the drop down for 'symbol' (between value and color ramp). Choose a light grey.
10. We will assign the same colour to ice shelf, tongue and rumple. To do this in 1 step, we can group the 3 values together. Do this by selecting the 3 values - press and hold Ctrl/Command and then click on the 3 values - once all 3 are highlighted, rick click and select 'Merge Categories', as shown below. Once the 3 values are merged, change the colour to white, or a different shade of grey to the land.
You should now have a much nice looking Antarctica!
There are a few different ways to access the symbology panel, and many different ways to symbolise data! This only explains one method.
Points
Next, we will display the research station points in a slightly better way.
Open the symbology pane for your points (either the shapefile or geopackage, if you have them both open) by opening the layer properties with right click-properties or by double clicking the layer.
First of all, see if you can change the colour and size of the points.
Your points should be symbolised as circles, and we will now try using different shapes. Click the 'Simple marker' in the small window at the top (highlighted below). This gives you many more options for customisation.
Try selecting different shapes in the window at the bottom of the pane (highlighted below). Which symbols do you think work best? You must always be thinking about legibility - the simpler a symbol is, the easier it is to see on a screen and on a map, in general.
You can also change the 'stroke colour' here. The stroke is the outline of the shape, as opposed to the 'fill' which is the inside. Similarly when we were editing polygons, you could have changed the stroke colour by going into this more detailed symbology panel.
Choose your favourite shape, colour and size, click apply, and close this panel.
As mentioned before, there are endless options for symbolising points. You can choose 3D shapes, photos, and as with polygons, you can choose 'categorised' to display the points in different ways depending on an attribute. For stations, this is often done with 'summer only' and 'year round' stations.
Polylines
Lines can be symbolised in the same way that instructions have been given for polygons and points. Go ahead and open the symbology panel for your contours, and try a few different colours and widths to see what you think works best. Blue colours are often used for Antarctica when the contours are over ice, but you can choose whatever colour you think best.
Have a play around with the further settings under the 'simple line' options as shown below. You can select dashed lines, and although they might not really work for contours, they can be useful for other line datasets.
If you have time left after this, try and display your research station points using the categorised symbology. Values such as 'seasonality', 'status', and 'type' should all show you interesting results which you might want to show on a map.
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