How does altitude affect baking and what adjustments should be made to recipes at higher elevations?

Altitude affects baking by causing changes in air pressure and moisture levels, which can lead to baked goods rising too quickly or not enough. At higher elevations, adjustments should be made to recipes by increasing the amount of flour and decreasing the amount of leavening agents, sugar, and liquid. Additionally, baking times may need to be adjusted to ensure proper doneness.