[contravariant]

I have to say the phrase 'isomorphic tunings' is very confusing if you have a mathematical background. It apparently doesn't refer to tunings which are effectively the same (not entirely what this would mean, I suppose you could swap a few strings).

[mrob]

Wikipedia calls them "regular tunings", which I think is clearer.

https://en.wikipedia.org/wiki/Regular_tuning

[elsherbini]

Totally, my mistake. The correct term is regular tunings, which yield an isomorphic layout on the guitar (well, it would if you had infinite strings). In plain english, the same shape always corresponds to the same intervals no matter what strings you are playing.

[Analog24]

Perhaps isometric would be a better description? We're probably getting into the pedantic weeds here though :-)

[osrec]

Well, this is HN, afterall :p

[dwringer]

It means they are effectively the same as you shift rightwards or leftwards on the neck. So you can play a G major chord, move the same exact shape "down one string" and now it's a C major chord. This is not a feature of standard guitar tuning.

[Sharlin]

I guess isomorphic tunings are isomorphic in the sense that you can move a fingering not only up and down the fretboard, but also from one set of strings to another, and the chord remains the same, just transposed.