A restriction map is a map of known restriction sites within a sequence of DNA. Restriction mapping requires the use of restriction enzymes. In molecular biology, restriction maps are used as a reference to engineer plasmids or other relatively short pieces of DNA, and sometimes for longer genomic DNA. There are other ways of mapping features on DNA for longer length DNA molecules, such as mapping by transduction (Bitner, Kuempel 1981).
Restriction mapping is a useful way to characterise a particular DNA molecule. It enables us to locate and isolate DNA fragments for further study and manipulation. The relative location of different restriction enzyme sites to each other are determined by enzymatic digest of the DNA with different restriction enzymes, alone and in various combinations.The digested DNA is separated by gel electrophoresis and the fragment sizes that have been generated are used to build the 'map' of sites of the fragment. The map lets us know 'where we are' in the linear DNA macromolecule.