Competitors might have a few seconds to secure the maps they see for the first time at the start, then it's off. Usually, about the only thing that stops a ski-o event is lack of snow. You could hardly see your map. The organizers decided on a mass start, otherwise the first skiers out would've had to break trail for everyone else. Once on the course the orienteer pits his wits and endurance against the terrain.
Controls are usually at locations along trails - the bend, the crossing, the top of the hill.
Sometimes meet directors augment the existing trail network with snowmobile tracks. When you're skiing fast you can lose track of things like trail junctions. It's the run fast, run stupid syndrome. What you want to do is memorize a piece of the map. Then you think about route choice.