Ddim is a diminished, spelled D, F and Ab. In Ukulele (low G) tuning (G3 C4 E4 A4) the easiest shape is 121x, which sits at fret 1, needs a barre across 3 strings at fret 1 and mutes 1 string. 12 positions for it are shown below, from the nut up to fret 13.
Notes and intervals
Note
D
F
Ab
Interval
1P
3m
5d
12 ways to play it
Ordered by how hard they are to fret, easiest first, one per position on the neck. Fret numbers are relative to the position marked beside each grid.
121xsits at fret 1, needs a barre across 3 strings at fret 1 and mutes 1 stringx545sits at fret 4, spans 1 fret and mutes 1 string78108sits at fret 7 and spans 3 frets108108sits at fret 8 and needs a barre across 3 strings at fret 8x141311sits at fret 11, spans 3 frets and mutes 1 string131413xsits at fret 13, needs a barre across 3 strings at fret 13 and mutes 1 string10141311sits at fret 10 and spans 4 frets7545sits at fret 4 and spans 3 frets754xsits at fret 4, spans 3 frets and mutes 1 string7548sits at fret 4 and spans 4 frets7848sits at fret 4 and spans 4 frets10810xsits at fret 8, spans 2 frets and mutes 1 string
Keys Ddim belongs to
Ddim is diatonic to 8 of the 96 keys this app knows, playing a different role in each.