I think a map of the fretboard could offer some interesting gameplay ideas. Here's mine (please do not be offended by my incredibly bad Paint skills).
Behold, my gameplay idea for a Guitar Fretboard (just gameplay!)
- Click image to enlarge.

Territories: 72
Bonuses: 25 (6 string, 12 fret, 7 note; see below)
You can attack either along the string (horizontal) or across the fret (vertical).
There are three types of bonuses, holding an entire string/row, an entire fret/column, or all of a note/colour.
Grey boxes are part of fret and string bonuses, but not any note bonuses.
The idea is that each colour is where each note (A, B, C etc) is on the guitar - each note occurs six times on the first 12 frets.
Blue = A
Purple = B
Red = C
Orange = D
Yellow = E
Green = F
Cyan = G
I figured it would be better not to include notes like F# and Bb etc, so that every territory isn't part of 3 bonuses, thus making some territories more important than others.
I ran the details through a bonus calculator and made a few adjustments. The calculator told me that the bonus for holding all of a colour would be +6. Another option for the colours/notes is to have like this, for example:
Any 3 of the same note: +2
Any 4 of the same note: +3
Any 5 of the same note: +4
Any 6 of the same note: +6
The good thing about the colours is that some bonuses lead more easily to another colour than others, for example it is relatively easy to invade Reds from Purples, but not Oranges from Reds.
Anyway, this is why I stay out of the Foundry
