In my forthcoming paper on teaching yourself to play the ʻukulele, I venture into similarities between guitar and ʻukulele chords. If you already play the guitar, thinking in intervals and chord shapes will give you a head start to playing the ʻukulele.
In the low G, C, E, A tuning, the ʻukulele equivalent of a guitar chord is a perfect fourth interval higher without the bottom two strings of the guitar (i.e. the 5th and 6th lowest strings). Thus if you play an D major chord on the guitar, the same shape on 
the ʻukulele will give you a G major chord, as G is a perfect fourth higher than D.
We are not talking about transposition but chord conversion according to shape, or more specifically, chord diagram.
Chords on the guitar that use the two lowest strings will simply “lose them” on the ʻukulele which has only four instead of six strings. For instance, the C major chord on the ʻukulele is derived from the guitar chord shape that is a perfect fourth interval higher — the G major chord. Only the top string is retained. Similarly the A7 and Am chords on the ʻukulele both have only one string depressed, equivalent to the E7 and Em chord shapes on the guitar respectively because the bottom two strings are non-existent.
In many ways, learning a new instrument is like learning a new language. If you already play a different instrument, youʻre constantly referencing what you know. Just like languages, you’re initially translating the vocabulary in your head. After awhile, you learn to think in that new language. For the guitarist who is learning the ʻukulele, chord shapes are the link between the two.
The following table shows the most common equivalent shapes for both instruments. Notice that they are a perfect fourth interval part.
| Guitar |  |
| Ukulele |  |