<P> Further inaccuracies may be deliberate . For example, cartographers may simply omit military installations or remove features solely in order to enhance the clarity of the map . For example, a road map may not show railroads, smaller waterways or other prominent non-road objects, and even if it does, it may show them less clearly (e.g. dashed or dotted lines / outlines) than the main roads . Known as decluttering, the practice makes the subject matter that the user is interested in easier to read, usually without sacrificing overall accuracy . Software - based maps often allow the user to toggle decluttering between ON, OFF and AUTO as needed . In AUTO the degree of decluttering is adjusted as the user changes the scale being displayed . </P> <P> Maps of the world or large areas are often either' political' or' physical' . The most important purpose of the political map is to show territorial borders; the purpose of the physical is to show features of geography such as mountains, soil type or land use including infrastructure such as roads, railroads and buildings . Topographic maps show elevations and relief with contour lines or shading . Geological maps show not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures . Maps that depict the surface of the Earth also use a projection, a way of translating the three - dimensional real surface of the geoid to a two - dimensional picture . Perhaps the best - known world - map projection is the Mercator projection, originally designed as a form of nautical chart . Aeroplane pilots use aeronautical charts based on a Lambert conformal conic projection, in which a cone is laid over the section of the earth to be mapped . The cone intersects the sphere (the earth) at one or two parallels which are chosen as standard lines . This allows the pilots to plot a great - circle route approximation on a flat, two - dimensional chart . </P> <Ul> <Li> Azimuthal or Gnomonic map projections are often used in planning air routes due to their ability to represent great circles as straight lines . </Li> <Li> Richard Edes Harrison produced a striking series of maps during and after World War II for Fortune magazine . These used "bird's eye" projections to emphasise globally strategic "fronts" in the air age, pointing out proximities and barriers not apparent on a conventional rectangular projection of the world . </Li> </Ul> <Li> Azimuthal or Gnomonic map projections are often used in planning air routes due to their ability to represent great circles as straight lines . </Li>

The scale of a road map indicates that 4