Seen from an airplane, small hills look like flat land.
Literal
Airplane [from-から] look [if-と], small hills [topic-は] flat-land [like-のように] appear.
Uses the conditional ~から見ると ('when you look from') to frame an aerial perspective. ~のように見える means 'looks like.' 丘陵 (きゅうりょう, 'hills') and 平地 (へいち, 'flat land') are formal geographic terms.