Multi map or multi floor navigation with a mobile robot.

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I'm trying one of my ideas of using a differential drive mobile robot for multi floor navigation.

Thinking of using a multi-map navigation approach, so that different maps are loaded for navigation depending on what floor the robot is present in.

I've checked similar answers here but what would help me more is if an overlay or a basic explanation of the idea is provided, maybe more inline with

1. what procedure should one follow to tackle multi-map navigation(if there exists any).
2. What ROS packages or implementation techniques could be used.

Thank you.