Think of a swimming pool with a shallow end and a deep end. the pressure of water on the floor at the shallow end is less than the pressure of water on the floor at the deep end. how is this similar to the way air pressure differs at different altitudes?

Air gets thinner as we go higher because there are less trees and gets thicker on ground level because of the abundance of vegetation.
Water is not condensed on the surface because it doesn't have any pressure acting on it vertically but gets condensed as we go deeper because its own weight acts as a force.
Both scenarios are similar.