http://kingsrow.uk/callouts/
here is a picture guide of the maps in overwatch which shows what all area's are commonly called in competitive play
Awesome link! It also leads to a lot of the other maps.
Let me add my input on the importance of map callouts. It should be well established among competitive players so there is a proper understanding of direction in game. Saying things such as "Top left" or "behind" can be too vague. Your teammates need to know exactly where to look when that pesky Genji is harassing your backline.
I paint my pictures with words and construct my buildings from thought.
It might not be exciting, but this might be a good subject for at least fireteam practice. Just taking a tour and learning to call map parts by the right name can be useful, but only if the whole team gets used to it and knows what the others mean.