If  we have a completely flat surface on a  planet..........     What  would the inhabitants  of that  planet  see ???    A hollow  bowl like valley   with  4 mountain peaks @ the  4  corners ?   Like  this  *  but here the sides  are straight and perpendicular  in that  case they  would have slopes....  it was difficult to  design the  exact shape ....😁   And  if we  pour  some liquid  say water on that  flat surface  how would it  stand  there ?