rough sketch
「下図」 has another reading with different meanings.
鉛筆で下図を入れる。
I'll put in a rough sketch with a pencil.
漫画家は編集者に下図を確認させた。
The manga artist had her editor check the rough sketch.
建築家が顧客に建物の下図を描いて見せた。
The architect drew a rough layout of the building and showed it to the client.