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For the construction of the world maps, the main projections generally used in atlases are:

(1) Zenithal,

(2) Mollweide's Elliptical,

(3) Mercator,

(4) Cylindrical Equal Area, Gall's and

(5) Sanson-Flamsteed.

Of these the Zenithal Projections are used for the world in two hemispheres, while others are used for continuous world maps. The choice of Zenithal for the world map lies in the fact that two maps are needed for showing the hemispheres and thus there will be less distortion in this than in the map in which the world is shown continuously. But there are certain purposes for which continuous world maps are useful, such as for showing the wind system, ocean currents, isobars, etc. On this ground Sanson-Flamsteed Projection may also be rejected because there is much more distortion along the margins of the map than in the other three projections. Besides, for the distribution maps of the world, the choice will be restricted to a few because only homolographic projections will be most suitable for them. In case the distribution of tropical and subtropical crops like rice, cotton, tobacco and sugarcane, etc., is to be shown over the world map, Cylindrical Equal Area Projection will be more useful than Mollweide's and Sinusoidal as in this projection within 3O degrees of the equator, distortion is much less and the meridians and parallels intersect each other at right angles so that the shape is relatively much more correct. Moreover, it is also very easy to construct this projection. On the other hand, when the distribution of temperate crops like wheat, is required to be shown on the world map, Mollweide's and Sinusoidal will prove better than the Cylindrical in which there is much distortion in the temperate region. Even of the two, Mollweide's will be more advantageous as it provides for less distortion than the Sinusoidal. Mercator's is very important in. that it is the only projection, which correctly represents compass bearings by straight lines from all points and as such, it is singularly chosen for communication and navigation maps.

So far as the regions stretching both north and south of the equator are concerned, the claims of all the world Projections may be considered. For an extensive region like Africa, which stretches equally north and south of the equator, Sanson-Flamsteed may provide the most appropriate graticule, which combines good shape with truly proportioned arc, though Equatorial, Zenithal and Cylindrical Equal Area are also used for it. Also for South America whose major portion extends south of equator, Sanson-Flamsteed is the best though conical and Boone's may be possibly used because the construction of Sanson-Flamsteed is comparatively more difficult than that of the Simple Conic with two Standard Parallels. For other areas like the Indian, Pacific and Atlantic Oceans, our choice may rest upon Equatorial Zenithal Equidistant or Equal Area Projection or Stereographic Normal Zenithal in which the equator is a straight line passing across the country.

North America and Eurasia in Northern Hemisphere and Australia and Oceania in Southern Hemisphere lie, more or less, entirely north and south of the equator respectively. For these we may select between Conical with two Standard Parallels, Boone's and Polyconic. For North America all the three may be suitable but for Europe only Conical with two Standard Parallels or Polyconic will be appropriate because east-west dimension of Europe is greater than north-south extension. Though in Boone's the amount of distortion increases towards the margins, the difficulty of greater dimensions along the base does not arise because of the curved meridians; so the projection has been generally applied for India and Asia by atlas makers. Zenithal Projections are suitable for those regions whose length and breadth are equal because the amount of accuracy decreases equally in all directions as the graticule is drawn from a central point along a line which passes vertically through the centre. For polar maps Zenithal are, therefore, as ideal as Cylindrical for equatorial lands, other things being equal.

Airways may follow more closely the greater circle routes. So Gnomonic Projection which is also known as Great Circle Projection is ideally appropriate for maps showing airways. But in. this projection scale is exaggerated away from the centre and therefore its use is restricted to a comparatively less extensive region.

For smaller countries like British Isles, Baltic States, France, Spain, etc., there is little difficulty in choosing a projection. Their extent is so small that projection which is easier to construct may be adopted. For the Baltic region and for France simple Conic with two Standard Parallels may be applied. Simple Conic with one Standard Parallel may be used for maps showing transcontinental railways, e.g., Trans-Siberian, or Canadian-Pacific etc., which may ideally correspond with the Standard Parallel along which the scale is true.

For one-in-million map and other Topographical Survey Maps none of these projections provide ideal conditions. A modified form of Polyconic known as International Map Projection has been applied for the former in which each sheet is drawn independently with its own meridian so that the combination of various adjoining sheets may be possible. A modified form of Cylindrical Projection is used for Topographic Survey Maps. The projections evolved for these large-scale maps lie outside the scope of the text.