I like to think of layer one as the “soil”—an excerpt from a source or my own thinking (whether as words, drawings, images, or audio) I initially capture into my notes. They are like the ground on which my understanding will be built. Layer two is “oil,” as in “I’ve struck oil!,” conveniently represented by black, bolded text. Layer three is “gold,” which is even more valuable, and shines in highlighter yellow in many apps. Layer four is the “gems,” the most rare and illuminating finds that I’ve distilled in my own words as an executive summary.
