Modify the topographic map using the fruits of projective layout 利用规划放线成果修测城市地形图
To make it easier to map the city , we will assume that all buildings are lying on a flat area block called a “ base tile ” 为了更方便的绘制城市地形图,我们假设所有的建筑都处在一个平面区块上,这个平面模型叫“底部地基” 。