The ability of a cell to respond to its environment depends on the actions of the proteins encoded by the DNA in the genome. However, most proteins don't work alone. They work with other proteins in teams called complexes. The principles of "mapping" are to figure out which proteins work together in complexes. Mapping can be done in different disease states or in the presence of different chemical drugs. The integration of the physical and genetic maps allows us to derive quantitative insights about how the biological functions of cells can be perturbed and restored.