Adding a polygon feature to a vector layer

In this recipe, we'll add a polygon to a layer. A polygon is the most complex kind of geometry. However, in QGIS, the API is very similar to a line.

Getting ready

For this recipe, we'll use a simple polygon shapefile, which you can download as a ZIP file from https://geospatialpython.googlecode.com/files/polygon.zip.

Extract this shapefile to a folder called polygon in your /qgis_data directory.

How to do it...

This recipe will follow the standard PyQGIS process of loading a layer, building a feature, and adding it to the layer's data provider, as follows:

1. Start QGIS.

2. From the Plugins menu, select Python Console.

3. First, load the layer and validate it:

   vectorLyr =  QgsVectorLayer('/qgis_data/polygon/polygon.shp', 'Polygon' , "ogr")
   vectorLyr.isValid()
   

4. Next, access the layer's data provider:

   vpr = vectorLyr.dataProvider()
   

5. Now, build a list of points for the polygon:

   points = []
   points.append(QgsPoint(-123.26,49.06))
   points.append(QgsPoint(-127.19,43.07))
   points...