Comment by nkrisc

If you were just using something kind of remote sensing technology to determine where people were in the building, but you didn’t know the layout, you couldn’t be sure. I’ve seen examples of using WiFi or other radio frequencies to spatially locate people through walls, but it doesn’t let you actually see what’s there.

So if you combine their position in the building with separately collected layout information about the building, you can better infer their activity.