Boss Keys style maps
Being inspired by Gamemaker's Toolkit's first season of its mini-series Boss Keys, which is a series that looks into the design philosophies of Zelda dungeons in terms of layout, I decided to do something similarly for the Metroid series. This idea was fueled by things like item randomizer algorithms and 100%-speedruns, because I wanted to find a way to chart out the areas of Metroid in an attempt to facilitate pathing and maybe even help Metroid fangame makers to think about design and gating in their games.
After starting with NEStroid, I figured on tackling Super Metroid next. Oh boy.
You'll notice that I used Cyrillic letters to connect the elevators and sector access points. There are so many in Super Metroid that I don't think there was really another way to do this.
Also, I decided to use Cyrillic instead of Latin or Greek because the Greek letters are dedicated to the Metroid designations of Metroid 2, and the Latin characters are more for important things like Save Stations, Map Rooms, Energy and Ammo Recharge Stations, teleporters in Hunters, and more.
Beyond that, Super Metroid has quite a bit of flexibility when it comes to destroying those "Bombable" blocks, so I had to go back in and analyze every instance of those blocks to test all the methods that can be used in order to break those blocks. So you'll see Bomb locks next to Power Bomb locks next to Screw Attack locks next to Speed Booster locks, quite a bit.
There was no real reason for me to separate Green Brinstar from Red Brinstar besides readability. They're not separated by any elevator.
And here we see two splendid examples of "the first time you go here, you need all these items, OR just this one other upgrade". On the left of the image, the "green bubble" room close to the Speed Booster and Wave Beam locations. In the middle of the chart, the long hallways in the middle of Norfair's map, which can all be shortcutted by the Speed Booster tunnel next to the Save Station.
Yes, there is some softlock potential early in this area if you fall past a certain ledge and don't have Morph Ball, High Jump, or Space Jump. However, a Wall Jump is still doable. If you got to this point without any of those items, chances are you're already a pro at Wall Jumping, so that should be no biggie.
Entering Maridia via the East Crateria elevator is more trouble than it's worth. Just backtrack to Red Brinstar and get to the glass pipe. The other route brings you there eventually anyway, only with some softlock potential if you don't have High Jump or Space Jump, or walljumping skills.
Yes, there is a softlock Save Room, past the point of no return.
Here's a condensed version of the above charts, showing what the whole of Zebes looks like in terms of item dependencies:
As open as the game seems to be, it's quite deceptively linear. The boss order will practically always be the same, given how one boss's treasure is required to get to one boss next. Observe:
You need the Morph Ball to get the Bombs.
You need the Bombs to get the Super Missiles.
You need the Super Missiles to get to Kraid.
You need to beat Kraid to get the Varia Suit.
You need the Varia Suit to get to Crocomire.
You need to beat Crocomire to get the Grappling Beam.
You need the Grappling Beam to get to Phantoon.
You need to beat Phantoon to get the Gravity Suit.
You need the Gravity Suit to get to Draygon.
You need to beat Draygon to get the Space Jump.
You need Space Jump to get to Ridley.
A lot of the stuff in between is just needed to get to the next big milestone. Any variance that lets you get another upgrade "out of sequence" usually will just be optional to actually completing the game. But the bosses will likely still be in the same order due to the level design making the previous boss's treasure a prerequisite to getting to the next boss.
Then again, all bets are off in a randomized run.