Panning (that is, clicking and dragging on the map to move around) is another area where the QGIS default behavior isn't quite what we want. QGIS includes a classQgsMapToolPan class, which implements panning; however, it also includes some features that could be quite confusing for users coming from Google Maps. In particular, if the user clicks without dragging, the map is re-centered over the clicked-on point. Instead of using classQgsMapToolPan, we will implement our own panning map tool. Fortunately, this is simple to do: simply add the following class definition to your lex.py module after the end of your MapExplorer class definition:

class PanTool(QgsMapTool):
    def __init__(self, mapCanvas):
        QgsMapTool.__init__(self, mapCanvas)
        self.setCursor(Qt.OpenHandCursor)
        self.dragging = False

    def canvasMoveEvent(self, event):
        if event.buttons() == Qt.LeftButton:
            self.dragging = True
            self.canvas().panAction...