These London maps illustrate the principle that, often, several maps are needed to get to a destination of interest. The map of the underground railway (“the Tube”) is used to get to a destination of interest such as a street address, shown on the street map. In genetics, two different kinds of genome maps are often useful in locating a gene, leading to an understanding of its structure and function.
[(left) © MAPS.com/Corbis; (right) Transport for London.]