For higher-res maps with amazing detailed analysis, I recommend Zone 0.

The following level maps were all created from ROMs of the game concerned by "Stealth" for the now-defunct website ssrg.emulationzone.org. As they are no longer easily available elsewhere online I felt it would be worthwhile putting them online myself.

Note that these maps do not include anything more than the "hard" level structure: things like springs, collapsible scenery, badniks, rings and floating or moving platforms are completely missing. This makes using these maps to plan your route more difficult than it could be. Note also that since the level appearance can change when you e.g. go inside the tree in Angel Island 1, these different images are sometimes found off to the side somewhere where they can look pretty silly. You may have to mentally reconstruct the images yourself.

Sonic The Hedgehog 2

Sonic The Hedgehog 3

Sonic & Knuckles