A contig (from contiguous) is a set of overlapping DNA segments that together represent a consensus region of DNA.[1] In bottom-up sequencing projects, a contig refers to overlapping sequence data (reads);[2] in top-down sequencing projects, contig refers to the overlapping clones that form a physical map of the genome that is used to guide sequencing and assembly.[3] Contigs can thus refer both to overlapping DNA sequences and to overlapping physical segments (fragments) contained in clones depending on the context.