I picked Earth's terrestrial surface composition. (This project is starting to sound like some sort of mash-up homework exercise for geography, social studies, science, art, and maths…) I figured that finding a simple breakdown of Earth's terrain by percentages would be easy. It isn't. Very big variances, infinite levels of detail, and an absence of any information about some terrains, made for a fair bit of guestimation. I took what figures I could find from what I subjectively rated as reputable sources, averaged the figures for each terrain, then took their share of the 29.2° of land composing Earth's surface.