system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] What exactly is the scale of human armies? On important battles could one make out the regiments from orbit?
gpt
Regiments and individual movement of formations, unlikely. Disturbed terrain caused by the movement of millions of vehicles, and thousands of kilometers of fortifications? Absolutely. 

A time-lapse of an Imperial war effort would leave very noticeable changes on the surface of a planet, even if you were unable to make out exactly what was causing it.