I’m wary of risking sanity by descending into flat earther territory online to find out their excuse for this one, but:
Where are the edges?
If the world is flat, either there’s physical edges or the world has an infinite surface area… Seeing as demonstrably neither are true, what’s their ‘reasoning’ around that one? 
Where are the edges?
A few years ago I stumbled into some flat earth videos on Youtube and I think their answer is that the edge of the disc of Earth is Antarctica. I mean, have YOU been there to confirm that there’s no edge? Given how restricted access is there, it’d be trivial to hide the edge. It’s probably the least difficult thing the Illuminati do.
It’s the same reasoning Ken Ham uses to disprove evolution: Did you see it happen? No? Case closed.
Just about all of science would be wrong if it was.
Um… NO! It’s four elephants on the BACK of one space turtle! Everyone knows that!
Flat Earth!
Note that “circumnavigating” the Earth is just walking in a circle around it. I like to imagine flat-earthers high-fiving each other when they figured out how circumnavigation works on a flat Earth.
Gus: We did it! Flat Earth can be circumnavigated!
Stan: But what about from North to South?
Gus: … Dammit Stan!
Yes, technically I don’t know that the Earth isn’t a hollow cylinder or something like that. But it’s obvious that the Earth curves, because distant objects fall away over the horizon. Also, if you go to the top of the mountain, you can actually see the Earth’s curvature.
In 240 BC, Eratosthenes not only knew the Earth was round* but calculated its radius to within a few percentage points of truth. In 2017… Teach The Controversy! ™
*technicaly, it’s an oblate spheroid.
Uni-Chelonian Heretic!
A bulged disc could explain the curvature that we see, though I’m not sure how they explain why the oceans don’t pool in a ring surrounding Antarctica.
My GPS still works.
Next!
The sun is a spotlight, apparently, according to these folks.
I’ve seen so many of their “proofs” in the last few weeks, it’s a wonder I can hold on to the last few shreds of my sanity.
TIL the Earth is a roulette wheel. Always bet on water.
Cell phones work off cell-phone towers, therefore so does GPS; no “satellites” required. According to them.
I’m not responsible for their delusions, or conspiracy theories, about how GPS technology works.
Indeed you’re not; I’m just filling you in on the joys you’re missing by not having any flat-Earthers in this thread. 
To make flat-Earthism work, I don’t think light can travel in a straight line. Nothing makes sense if it does. I’m not sure what kind of wiggly, arbitrary path it takes, but it can’t be straight.
It’s interesting to try to figure out convoluted explanations to allow things like flat-Earthism to be consistent with reality, but these people aren’t even trying. The Sun would not only have to be a spotlight, it would have to have a mask that shaped the light coming out. And not only would the Sun move during the course of the year, the shape of the mask would also have to change as well. (Even if light also travels on a curved path.) I suppose there’s also the small issue that the shape of and distance between the continents would be totally screwed up - and easily disproved by anyone who traveled anywhere, so anyone who sails or travels via airplane would have to be part of the same conspiracy to which all astronomers, geographers, telecommunications experts, etc. belong.
Simple. If the earth were flat, cats would have knocked everything off it by now.
