It's shape.
Is it that you thought the earth was shaped just like the North Polar Azimuthal Equidistant Projection ?
(The one showing Antarctica as the ice ring.)
Some FE's like this one !
Or did you think the earth was shaped just like the Bipolar Projection ?
(The one showing no ice ring but showing Antarctica as a continent. )
Tom Bishop likes this one !
Which one of the above did you think was a map of the flat earth and that convinced you the earth was flat ?
Or was it some other map or some other reason that convinced you that the flat earth model is correct ?