Scale also causes mis-perceptions. If there's nothing near the object for which you know the size (a person, some trees, a building) it's very easy to misjudge size.

For example, I'm sitting in a motel room in Las Vegas (national accounants' conference, no say in the location, and I'm required to attend because I chair our state's committee; my impression so far is that if Nellis AFB needs a new weapons range, I know where they can get one without wasting any perfectly good desert.)

But I digress. As I look out my window, I can see the mountains. There are no trees on the mountain, and no buildings anywhere near; there's also what appears to be a good amount of desert between the edge of town and the beginning of the range. Based on my perceptions and affected by the height of similar-appearing mountains in Tennessee ("similar" meaning how far above the plain they appear), I'd guess these mountains are about 4,000 feet high, and about 10 miles away. However, I'm willing to bet (hey, it IS Vegas) that I'm at least 10,000 feet and at least 40 miles off.