Adding Points

The following map tool allows the user to add a new Point feature to the given layer:

class AddPointTool(QgsMapTool):
    def __init__(self, canvas, layer):
        QgsMapTool.__init__(self, canvas)
        self.canvas = canvas
        self.layer  = layer
        self.setCursor(Qt.CrossCursor)

    def canvasReleaseEvent(self, event):
        point = self.toLayerCoordinates(self.layer, event.pos())

        feature = QgsFeature()
        feature.setGeometry(QgsGeometry.fromPoint(point))
        self.layer.addFeature(feature)
        self.layer.updateExtents()

As you can see, this straightforward map tool sets the mouse cursor to a cross shape, and when the user releases the mouse over the map canvas, a new QgsGeometry object is created that represents a point at the current mouse position. This point is then added to the layer using layer.addFeature(), and the layer's extent is updated in case the newly added point is outside the layer's current extent.

Of course, this map tool...