Source: RotK... maybe movie!verse
Disclaimer: Tolkien drew up the grand battle plan, Kortirion outlined a skirmish
The shortest distance between two points is a straight line... tutors had drilled that into him. They also introduced him to maps; he’d been fascinated by stacked lines that became hills; others that were rivers, coasts, routes to unknown lands… All this knowledge... he was a captain; a man of plans and strategies that led his men by the safest paths - was this come to nothing?
Now the shortest distance was his only route, a line spread painfully thin across the Pelennor trotted forward. The distance from desperation to death became perilously narrow. He could but hope the line held.