An undefined 'sort by' category that sorts maps by.. what? Possibly some kind of hidden number generated from some mysterious property.

Where did you find this "sort by" ?

As he says: when you sort maps, you have 5 options: 4 named and one empty.

The empty one is quite similar to the reverse of map age, but it isn't:
* The older maps aren't exactly ordered by map age (e.g. some maps of 2012 appear before maps from 2011)
* It places Drakemor's World (2012) first, just before the oldest maps (2009)
* Every so often a random much more recent map is placed between older maps. e.g. "first page" (first 100) has maps from 2014, 2017, 2022 inbetween mostly maps from 2012 and earlier.

I have a hypothesis. I think this might be maps sorted in order of how long it's been since they were last updated. I came to this conclusion by skipping to the last page where I noticed a few maps by AbsolutelyEthan and I know he's been updating his maps recently.

the 19th map on the page is papa mersh's map which came out in 2021. I find it hard to believe that there are just 18 maps that haven't been updated since that one came out.

I also have proof that it's not the case since some of my maps are listed before others of mine that I know I haven't updated since the later ones came out.

Edited 10/7/2022 00:40:03

average rating
your rating
alphabetical
number of territories
map age

Hmm good point EIGBM. I didn't notice that map first time round.

The maps are ordered not from the moment they went public but from the date they were created to be developed.
Some maps take longer than others to be finished.

Edited 10/8/2022 22:11:46

PapaMarsh's account was created in 2019 though LionHeart, so that hypothesis doesn't work either.

An insight after monitoring the mystery sort for a few hours.

The mystery sortings change with time with a peculiar pattern:
- a few (<10) maps may change their postion drastically (500+ or even 1k+ positions) within hours in both directions
-- new postions may be in the middle of the pack or at the sole bottom
-- maps may revert their position back with another major swing
-- those changes are not in line with ratings sort changes by magnitude, which are all <70 positions
- a few (<10) maps may also change their postion slightly (<10 positions)
- other maps usually change their position just because of the changes above

Here is a snapshot of mystery ranks of the maps, which have significatly changed position in 4 hours.
Notice the Clue Special War map, at one point it became the last ranked map in the mystery sort and then it returned to the original position.

map_name			T0	T0+3h	T0+3.5h	T0+4h
Testopia			21	21	21	625
Race to the Island - 2.0	2382	1346	1347	1346
GodStorm			20	20	20	622
Elsass Frei			2374	1343	1345	1344
Element				2378	1344	1346	1345
Economic-Centers		2391	1348	1348	1347
Clue Special War		1742	1747	2653	1745

My guess is that the mystery sort is actually "no sort" and the results are some random noise in database.
Usually databases, when no sorting is specified, tend to return data in the same order, but this is never guaranteed. Maybe someone who knows databases better, may confirm or invalidate whether the observable patten is consistent with such databases' behaviour.

Also one might want to check the "new maps" filter with mystery sort.
That way it is easier to localize the changes.
Of that short list the 'United Kingdom of Israel' and 'Uruguay Small' maps are constantly switching places.

maybe it is sorted by number of players currently with a game on that map?

That doesn't match up with the list that Fizzer gave out in the list of 11 most played maps UnFairerOrb76.

Today Fizzer commented on the mystery sort during his AMA.

Recap of what he said:
- The mystery sort a relic from the times, when there were like 12 maps in total and it was the manual sort by Fizzer in they way he believed the maps should be displayed on the page.
- Since then it was not maintained, should not exist anymore and probably might get removed.