如果把地图分成块，只筛选范围覆盖的块中的单位，这样就可以减少很多不必要的筛选。四叉树可以有效解决这个问题。

树的每一层都把地图划分四块，根据地图尺寸来决定树的层数，层数越大划分越细。

当需要对某一范围的单位筛选时，只需要定位到与范围相交的树区域，再对其区域内的对象筛选即可。(If you map the map into blocks, you filter only the units in the block covered by the range, thus reducing many unnecessary filters. Four fork tree can solve this problem effectively.
Each layer of the tree divides the map into four blocks. The size of the tree is determined by the size of the map, and the larger the number of layers, the smaller the division.
When you need to filter a range of units, you only need to locate the tree area that intersects the range, and then filter the objects in the area.)