text: The advantage of OM over traditional mapping techniques is that it preserves the order of the DNA fragment, whereas the order needs to be reconstructed using restriction mapping. In addition, since maps are constructed directly from genomic DNA molecules, cloning or PCR artifacts are avoided. However, each OM process is still affected by false positive and negative sites because not all restriction sites are cleaved in each molecule and some sites may be incorrectly cut. In practice, multiple optical maps are created from molecules of the same genomic region, and an algorithm is used to determine the best consensus map.