This quick & dirty diagram describes how many "steps" a magic item is weakened by across the planes, as well as how far certain spells can reach. I had a hard time understanding the official art that shows this, so made my own.
2e - quick & dirty planar diagram for magic adjacency
2e - quick & dirty planar diagram for magic adjacency
C&C/D&D-related writings, Cortex Classic material, and other scraps: https://sites.google.com/site/x17rpgstuff/home
Class-less D&D: https://github.com/ssfsx17/skill20
Class-less D&D: https://github.com/ssfsx17/skill20