For data compression, every codding that I've seen is binary. It means we convert a language with $N$ symbol size to a language with $M=2$ symbol size. For example, in Huffman coding, the goal is to find a binary coding ($M=2$) for English language ($N=26$).
If $M$ is not equal to $2$ and have a value larger than $N$, is there any method to find good coding (or optimal coding) for compression? Is there any research for this type of problem?
Is it a right assumption that when the target symbol size is larger, the goal is to find a map from a subset of source symbols to one target symbol?