I’m sure there’s more logic to it, but there are twelve notes in the chromatic scale, so six rows of four gets you two octaves. Also putting them in rows of four means you get a nice interval (a fifth?) if you go down vertically.

Thirds vertically. Semitones go horizontally.

The fifth is a knight's move away down, or up and to the left. Like other isomorphic layouts, it conceptually tiles infinitely in all directions.

if you tap the '-' key on ur keyboard it shows an overlay in red and green with the steps down and up which i've been using as a transposition aid

this still requires that you know how many semitones of interval you want