Practical Manual - Malareo

Next you will create a line layer (line layers are also refered to as polyline layers, poly meaning many) for
the roads.
To do this, add the layer HC_roads to the legend. (This is a blank line layer with attribute fields called
Road and Length)
Scale and accuracy
An important consideration when digitizing , is the scale (Zoom) at which you will digitize. This is highly
dependant on the needs tof the work you are doing and the required precision. If you zoom out too
much you will not be able to see details in an image. But is you zoom in too much sometimes depending
on the quality of an image you will also not be able to see a lot.
This is shown below:
Too zoomed out
Too Zoomed in
On the image on the left it is too zoomed out to allow for accurate digitizing (You need to be able to
accurately or precisely follow roads. On the image on the right you are so far zoomed in that the image
appears distorted. Therefore a balance needs to be found.
It also helps to maximize the size of your QGIS window. This gives you a larger view of the layers.
Maximize your GIS window. In order to set your zoom type 1:500 into the zoom window in the status
bar at the bottom of the QGIS window. Of course if you are digitizing at a provincial level you would
zoom out a lot more 1:10 000 for example
In this case 1:500 is a reasonable scale to digitize at as it allows objects to be seen clearly.
QGIS for Malaria Page 25