Mapping is the process of making a representative diagram cataloging the genes and other features of a chromosome and showing their relative locations. Cytogenetic maps are made using photomicrographs of chromosomes stained to reveal structural variations. Genetic maps use the idea of linkage to estimate the relative locations of genes. Physical maps, made using recombinant DNA (rDNA) technology, show the actual physical locations of landmarks along a chromosome.
The process of establishing the spatial relationship of landmarks within DNA is called mapping. Such landmarks can be genes or regions that vary among individuals. Mapping can involve simply ordering such landmarks, or in some cases precisely determining the spacing between them. Cytogenetic maps give the order of stained chromosome bands. Genetic maps represent the positions of polymorphisms--regions where the DNA sequence differs among individuals. Physical maps depict the actual physical locations of landmarks along a stretch of DNA.- Eric D. Green, M.D., Ph.D.