Well, from personal experience, from science, from math, from the fact that long bridges are wider at the top than at the bottom, from the fact that the sun doesn’t disappear due to perspective – it clearly sets and rises as you can see for yourself, from the fact that I can see a ship sail out to see and disappear below the horizon, from the fact that in the middle of the Lake Pontchartrain bridge for 8 miles you can see neither shore, from the fact that that in the middle of the ocean you can see no shore…. what makes you think it’s anything other? Because it always “looks” flat to you?