4. Digitising Vector Data

Duration: 10 minutes and 20 seconds

Country: South Africa

Language: English

License: CC - Attribution Non-commercial No Derivatives

Genre: Instructional

Producer: Chief Directorate: Spatial Planning & Information, Department of Land Affairs, Eastern Cape, South Africa

Views: 132 (13 embedded)

Posted by: giacomo on Mar 30, 2010

Learn how to create and edit vector and attribute data. In the previous two topics we looked at vector data. We saw that there are two key concepts to vector data, namely: geometry and attributes. The geometry of a vector feature describes its shape and position, while the attributes of a vector feature describe its properties (colour, size, age etc.). In this section we will look more closely at the process of creating and editing vector data – both the geometry and attributes of vector features.

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Hi, my name is Tim.
Welcome to the fourth topic in our Gentle introduction to GIS series.
In this topic we will explore vector data capture.
We will see how you can digitise your own point, polyline and polygon features.
And record attribute data for your newly captured features.
Let's take a closer look!
The first thing we will do is add some layers to our project so that ...
... we can have something to orientate ourselves with while we are working.
To do this, we will use the 'Add Vector Layer' option on the toolbar.
Click on the icon and in the file dialog that appears, ...
... move to your local data directory which is under: ...
... C: ...
... program files ...
... Quantum GIS ...
... Gisdata ...
... local.
Now you should see a list of vector layers.
Click the 50k_contours name and then click open.
The layer will be added to the map view.
Now repeat the process for the following layers: ...
... 50k_roads ...
... 50k_rivers ...
... 50k_inlandwater.
You should now have a nice looking collection of layers in the map view.
We are going to make a new vector layer called: mytrail.
To do this, click on the “New Vector Layer” icon in the toolbar.
Now choose 'line' for type.
Now we will create some attributes that will describe the line features we create.
For this exercise, we will be demarcating a hiking trail for tourists, ...
... so we will record 3 pieces of information for each trail: ...
First we will record the Name: a string (of text) which contains the name of each trail.
Type 'name' in the name field, set the type to 'string', finally click on the 'Add Attribute' icon.
Next, we are going to create field called Length.
In the Name box, type Length.
Then, set the Type to Real.
A Real is another name for a decimal number ...
... and that will describe how long each trail is.
Type 'length' in the name box, set the type to 'real' and then click on the 'Add Attribute' icon.
Difficulty: an integer (whole number) that describes how difficult the trail is.
Type 'difficulty' in the name field, ...
... set the type to 'integer' and then click on the 'Add Attribute' icon.
Now we have defined three fields for our attribute table. Name, Length, and Difficulty.
Click OK now to move on to the next step.
You need to give a filename that will be used to hold your new layer's data.
Let's call it mytrails.shp.
Now press save.
You will see your new layer has been added to the legend.
You will notice also that nothing shows on the mapcanvas ...
... that's because we have not created any features yet!
Let's create one now!
To do that, we need to enable editing first.
Click on the mytrail layer to make sure that it is the active layer.
Now click on the 'Toggle Editing' icon in the toolbar.
You will see some of the other tools on the toolbar now become active.
Click on the capture line tool and then start drawing a line on the map to create your first hiking trail.
You will notice that after you click once on the map, ...
... wherever you move the mouse the line will follow.
Each time you click, you add a new vertex for your line.
To finish your line, click with the right mouse button like this!
A new dialog will appear.
Can you see that it is asking us to fill in for the field names we defined earlier?
Let's give our trail a name: Klipspringer Trail ...
... and a length of 4 (km) ...
... and a difficulty ...
... a rating from 1-5 of how hard it is to walk the trail.
Since this is an easy trail we will give it a rating of 2.
Now click "ok" to add your attributes to the feature.
Try to add a few more trails, to create a nice hiking network for tourists.
now save your work by clicking under toggle editing tool once again.
Press "save" when QGIS asks you if you want to save your work.
Congratulations, you have just created your own vector layer.
You can now use the skills you learned in our previous tutorials to set the symbology of your trails based on their attributes.
So there we go; a tourism map we can give out to visitors who want to go hiking in the area.
That brings us to the end of this screencast.
In our next screencast we will take a look at raster data.
See you next time!