u/Bertieeee

I'm trying to understand the terrain layout when using a combat patrol map and I'm a bit confused. My understanding is that the grey rectangles are terrain areas, the items are ones that block visibility and the yellow ones don't block visibility but do provide cover. This doesn't seem right however, as I thought cover was determined by terrain area rather than being behind a specific (in this case yellow) piece of cover. If that's try however it would make the yellow items redundant, unless they're there purely for decoration. Could someone clarify how it works please?

Thanks