一个很好的调用了GOOGLEMAP的API的示例程序，大家可以很好的学习，里面包含地图的显示，反向地理编码等源代码，对XCODE开发者有很大的借鉴意义。-The sample program calls the API of Google Map. We can learn a lot from this example, which contains the map display, reverse geocoding and so on. It will help the developer

抽象类Shape，抽象方法：计算面积和显示面积，派生子类矩形和三角形-Abstract class Shape, abstract methods: calculating the area and display area, derived subclass of rectangular and triangular