The first reference genome sequences were entirely linear from a single or few individuals, but such a representation is not sufficient for encompassing all of the genomic variation present in a population. The human reference GRCh37 adopted a graph-based representation, by introducing the concept of alternative loci, which was expanded in GRCh38. Uptake of these graphical representations has been slow, in part because of a lack of tools to process the data in this form.
