I dont know which website to go to... this theory is from my own brain, perhaps read somewhere or someone taught me but long ago forgotten how I got this info. has to do with the angles you are viewing at and the distance you are viewing from.
but if you go and look at one of these fields you will find out about perspective. art, photography or architecture. people standing on the moon will also see that it's flat. but if you raise the high enough away/far enough away, they will see the curvature. have to remember, our perception is quite small compared to the whole planet. If your hand the size of the planet, then you will see the curvature easier. now it's the other way around. the planet outsizes everything that we are built to perceive.