def zoom(self,way,step=1):
        if way=="+":
            self.zoomlevel = self.zoomlevel + step
        elif way=="-":
            self.zoomlevel = self.zoomlevel - step
        else:
            self.zoomlevel = step
        if self.zoomlevel > self.zoom_max: self.zoomlevel = self.zoom_max
        elif self.zoomlevel < self.zoom_min: self.zoomlevel = self.zoom_min
        self.load_map()