Circle of fifths

The map every key lives on

The circle of fifths arranges all twelve keys in order of sharps and flats. Move clockwise and you add a sharp; counter-clockwise, a flat.

How to read it

C      no sharps or flats
G D A E B F#  add sharps
F Bb Eb Ab Db Gb  add flats

Why it matters

It's the cheat code for key changes, transposing, and knowing which chords belong together before you even play them.