Change map layer transparency

Map layer transparency allows you to change the opacity of a layer, so the items behind it are visible to some degree. A common technique is to make a vector layer polygon partially transparent in order to allow the underlying imagery or elevation data to add texture to the data.

Getting ready

In a directory called ms, in your qgis_data directory, download and extract the following shapefile from

https://github.com/GeospatialPython/Learn/raw/master/Mississippi.zip.

How to do it...

The process is extremely simple. Transparency is just a method:

1. First, we load the shapefile layer:

           lyr = QgsVectorLayer("/qgis_data/ms/mississippi.shp",
                                "Mississippi", "ogr") 
   

2. Next, we set the layer's transparency to 50 percent:

           lyr.setLayerTransparency(50) 
   

3. Finally, we add this layer to the map:

           QgsMapLayerRegistry.instance().addMapLayer(lyr) 
   

How it works...

If you set the transparency to 100 percent...