Before discussing altitude bands, it is useful to define reference level first.
Here we have drone bands as proposed by Amazon for its commercial drones rendered above Bellevue, WA, US. Obvious nonsense as they won't even be able to dodge trees. Personally I am not surprised nobody wants to loosen air traffic laws seeing such misguided proposals from what is claimed to be 'key players on the market' - particularly that I have warned them over a half year ago about inconsitencies and my willingness to collaborate.
This is why I am testing my implementation of global virtual airspace for autonomous drone navigation.
1. Grand Canyon, AZ, US
2. Sobótka mountain, S-W Poland (with a few airspace elements in the background)
3. Bellevue, WA, US
Blue net is USGL for symmetric navigation properties based on 10m DEM satellite radar and airborne LIDAR data.
Ground level is generated by obeying a few simple geometric principles that guarantee an automated system with specified climbing and cruise speed capabilities will be able to navigate safely in all directions (here 50mph, 1:10 climb slope, 1.12 max G factor).
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Actually I had FL implemented in FLEXIPILOT around 2011 as auxiliary altitude control logic. Flown once above trees at proud FL-1 in non-standard atmosphere.
That's a bit like the transition altitude in manned aviation, but the other way. That's where everyone sets the same altimeter setting and starts reporting flight levels. https://en.wikipedia.org/wiki/Flight_level You need to start posting this idea everywhere to establish prior art, its a good idea and will be poached by one of the big operators.