Elevation gain is the "up" for the day, how many feet climbing will be done on the day's route. Don't let the numbers scare you, the gain is over the entire day's mileage. You could climb 100 feet in two miles and barely notice it, but that is 100 towards the gain. It is computer generated based on GPS so every little rise ( 10, 15, 5, ect) is added on. I don't know the exact route but I would be surprised if any single climb would be more than 800 feet.