Set Screen Size To Only Be Wide?

Hello sorry if this is in the wrong place, if it is please remove it. Anyways my question is can I set the screen to be only playable when you turn your ipod/ipad horizontally? I've seen many games like that in the past, and I was wondering if Unity or Xcode can do that. The reason why I ask is because I've seen lot's of tutorials of games made with Unity, but all of them have been played vertically and not horizontally. I only want my game to be played horizontally for certain reasons. Anyways thanks for reading.