I've seen the topic come up a few times about how mappers keep organized while making nonlinear doom maps, so I figured I'd share some of my layout scribblings I've made over the years. I'm a fan of drawing arrows and jotting down notes onto a screenshot of the layout while brainstorming routes the player might take through the level, generally after I have a basic outline of the map but before I've committed to any proper detailing. Examples:
FCFF MAP01:
FCFF MAP06:
WORMWOOD MAP02:
WORMWOOD_EU MAP04:
MAGNOLIA MAP31:
MAGNOLIA MAP03:
WORMWOOD ]|[ MAP03: