Noisy Map Maker

I made a spreadsheet (it's a Google Sheet) that takes a dungeon map like this one:

Raw map data

...and turns it into an imperfect, noisy dungeon map handout for your players. Naturally there's lots of ways to introduce noise/errors to an image, but I wanted one that was solveable by clever players. That is, it'd still have some use if they couldn't solve the puzzle, but if they could, they'd know the dungeon layout.

(in this case, not the presence of doors or walls dividing adjacent rooms, as the map scale is 10 ft per cell. But you could make a map to a different scale)

How it works is by assigning a random number from one of two lists to a cell, based on whether the corresponding cell for the true map is blank or not. The two lists follow / don't follow a simple mathematical rule. Then a simple conditional formatting rule fills the cell based on whether the number is above a certain threshold. The conditional formatting creates the "noise", while cracking the rule gets you back to the true underlying information.

The easiest version of this puzzle just uses two adjacent sets of integers. You can even let players have control over the conditional formatting if a laptop or tablet is available, letting them home in on the correct threshold:

Numbers in [0,255] / Numbers in [256,512]

A simple divisibility rule is of middling difficulty.

Divisible by 3 / Not divisible by 3

Probably the hardest of the three pre-populated options is prime numbers. Though if you used this one, you could be sneaky here and indicate secret doors or similar with a 1, as 1 is neither prime nor composite.

Composite numbers / Prime numbers

You can download and mess around with the sheet, defining your own number lists (and associated rule to crack) and tweaking the conditional formatting threshold to have the right amount of noise. If you use this in a game, let me know how it goes!

Just remember the two lists must have different averages, otherwise the conditional formatting applied to the cells won't tell players much. A list of the first 1,000 even numbers and the first 1,000 odd numbers will look completely random if the conditional formatting rule is "colour cells with value > 1000". The goal is to look sufficiently nonrandom so as to tip off the players there's actual meaning to decipher.

But diegetically, what is this handout anyway?

d6	Reason for the map
1.	An ancient alien scannerbot, caked with dust, has done a geophysical survey of the dungeon. Its memory is corrupted, but its hologram display function still works. The map is unlikely to include recent dungeon extensions or geologic shifts.
2.	A room has a huge crystal, glowing amber, set in the ceiling. Dust motes hover in the light, apparently trying to tell you something. They respond to your thoughts more than they do drafts of air, their motion growing less random the more you concentrate. In this case the numbers aren't literal, decoding them represents this concentration.
3.	Extremely paranoid da Vinci-type gnome was the dungeon mapper for an adventuring party, disguising her findings as apparent gibberish numbers. Her skeleton lies in a trapped secret corridor, her cipher too devious for her party to decipher and come to her aid. Her worldly possessions, including the journal with this map, are for sale at an auction.
4.	An imp bound in chains of rock-salt sits impudently in a glowing magic circle. Eager to tempt the party into a dark deal he quickly pens the map in immaculate calligraphy for them. He promises them the trick to reading it, if only they would release him.
5.	Each number is actually meaningful. An ethereal telepath-spider unable to sense the physical world made the map to chart what it perceived as the dungeon layout. The map is a hovering blue tapestry, that can only be manipulated by ghosts and force effects. The dungeon is enchanted such that if two creature stand in spots with the same number, they can see through eah other's eyes and telepathically communicate. There is no saving throw to resist this effect, but moving to a different spot breaks the link.
6.	A colossal brain-eating catfish lurks in a cavern behind a secret passage. They have seeded the dungeon with clues, in the hopes of luring only the most intelligent, piquant brains to their demesne.