有些数字很容易解释

• MeanRadiusEarthInKm = 6371(根据 IUGG)

• MeanRadiusEarthInKm = 6371 (according to IUGG)

DegToRadDivisor = 180/PI = 57.2958

DegToRadDivisor = 180/PI = 57.2958

再次，缩放级别每一步都将尺寸加倍，即将缩放级别增加屏幕尺寸的一半.

And again the zoom level doubles the size with each step, i.e. increase the zoomlevel by one halfs the size on the screen.

zoom = 8 - log(factor * dist) / log(2) = 8 - log_2(factor * dist)
=> dist = 2^(8-zoom) / factor

从数字中我们发现缩放级别 8 对应的距离为 276.89 公里.

From the numbers we find that zoom level eight corresponds to a distance of 276.89km.