Hole lengths shown on your scorecard are derived from the course maps submitted by users. The fairway appears as a gray line going from the teepad to the basket. This is the line used for measuring the distance. On holes with doglegs, the dogleg is factored into the distance calculation.

On this hole, the distance of 341 ft includes the dogleg shape. This ensures that distance measurements are accurate even for oddly shaped fairways. 

If there is no map for the hole you can create one: Create a course map in UDisc.