Physical mapping involves assembling the order and distance of genetic markers directly from genomic DNA without cloning. There are several methods for physical mapping, including restriction enzyme fingerprinting, marker sequences like STSs and SNPs, and hybridization assays. The goal is to construct a physical map that reflects the actual order of genes and markers along chromosomes. Modern techniques like optical mapping and radiation hybridization have allowed constructing high-resolution physical maps without cloning by analyzing single DNA molecules.