平ら and 坂: a level path, a slope, and a flat board’s orientation
Compare a level path with a sloping road, then use a flat board placed at an angle to separate surface shape from placement.
A level condition of a path
For a path, 平ら, read たいら, can describe a level condition. この道は平らで歩きやすいです。 says that this path is level and easy to walk along.
平らな場所に荷物を置きました。 says that someone placed luggage on a flat area. Read the area’s condition with the past action of placing the luggage.
A path that changes elevation
坂, read さか, means a sloping path. 長い坂を上りました。 says that someone went up a long slope. 長い gives its length, while 上りました gives the direction traveled.
真っ直ぐな坂道もあります。 says that some sloping roads are straight. Having a slope and having bends are separate properties.
A flat surface and its placement
平らな板を斜めに置きました。 says that someone placed a flat board at an angle. A flat surface and a tilted placement can coexist.
坂の傾き describes a path’s slope, while 板の表面は平らだ describes the board’s surface shape. Do not replace 平ら with necessarily horizontal for every object.
Is 平らな板を斜めに置きました。 contradictory?
Show the answer and why
No. It describes the board’s flat surface and its angled placement separately. Both can hold at the same time.