Mapping covers a variety of technologies but they all aim to locate something "small" in something "large". One such technique cuts long DNA into fragments with restriction enzymes at restriction sites. This is done with two or more different enzymes, each with its own specific recognition pattern, singly and doubly (maybe triply). The bioinformatics problem is to recontruct the positions of the sites on the original DNA given the measured fragment lengths [Allison & Yee]. The problem is made difficult by the limited precision of the experimental data. The fragments between the sites are, hopefully, small enough to be sequenced by other means. The site positions plus the fragment sequences yields the complete sequence of the original long DNA.