The higher the altitude, the lower the air pressure. While this is an excellent environment for training athletes, it is a difficult one for baking recipes.
Baking depends on the specific interactions of several kinds of ingredients: flour, leavening, fats, liquid.
To complicate things further, individual microclimates vary greatly in the mountains, so the adjustment that works for you may not work for your neighbor down (or up) the road.
These charts are meant as a starting point, to help you convert recipes. Different types of baked goods need different adjustments, and we offer suggestions about where to start further on including adjusting chemical leavens according to altitude and baking cookies at high-altitude.
It may take a few tries to get results you’re happy with; if possible, try to adjust only one ingredient at a time, so you can isolate the effect it has. Be sure to keep notes on what you’ve done, and try the smaller adjustments first when a range is given.