<Li> Combination of the above: the scale depends on latitude only, not on longitude or direction . This applies for the Mercator projection in normal aspect . </Li> <Li> Scale is constant along all straight lines radiating from a particular geographic location . This is the defining characteristic of an equidistant projection such as the Azimuthal equidistant projection . There are also projections (Maurer's Two - point equidistant projection, Close) where true distances from two points are preserved . </Li> <P> Projection construction is also affected by how the shape of the Earth or planetary body is approximated . In the following section on projection categories, the earth is taken as a sphere in order to simplify the discussion . However, the Earth's actual shape is closer to an oblate ellipsoid . Whether spherical or ellipsoidal, the principles discussed hold without loss of generality . </P> <P> Selecting a model for a shape of the Earth involves choosing between the advantages and disadvantages of a sphere versus an ellipsoid . Spherical models are useful for small - scale maps such as world atlases and globes, since the error at that scale is not usually noticeable or important enough to justify using the more complicated ellipsoid . The ellipsoidal model is commonly used to construct topographic maps and for other large - and medium - scale maps that need to accurately depict the land surface . Auxiliary latitudes are often employed in projecting the ellipsoid . </P>

Map projections which preserves distance from a single location to all other locations is