Though a globe model of the earth is the most common version of the earth's surface, it's often not practical for many of our needs.
That's why maps are created for different purposes, which use map projection to depict the earth's surface on a plane using a wide variety of scales. Digital interactive maps also use map projections to present data on a computer screen.
Different maps use different map projections based on what purpose the map will serve and the scale that's suitable for the purpose. For example, a type of map projection may show severe distortions while mapping the whole country, but may serve as an excellent choice for a county's detailed map that aims to cover a large area. The type of map projections also influences some of the design elements of a map. While some are suitable for small regions, some other projections are good for mapping areas with a huge north-south or east-west extent, or to cover all countries of the world.
Map projections are classified based on:
Distortion characteristics: Some projections often need to show a particular area or its relative size accurately for distributions or other phenomena. These are called equivalent or an equal area projection. The Lambert Azimuthal projection that maps a sphere to a disk, and accurately shows all regions of the sphere is an example of this category. However, this equal area projection fails to represent angles with accuracy.
The Albers projection is another instance of equal area map projection that utilizes two standard parallels. Despite no preservation of scale and shape, the distortion in this case is found to be minimal between the standard parallels.
Conformal projection: These projections maintain angular relationships and show accurate shapes while covering small areas. Such maps are useful for navigational or meteorological purposes where angular relationships are important.
Equidistant projection: Maps that maintain accurate distances along given lines or from the center of the projection are based on this principle of equidistant projection. Such maps are used for navigation and for radio and seismic mapping. The Equirectangular projection and the Equidistant Conic projection are two examples of this category.
Azimuthal (or zenithal) projection: A projection that maintains accurate angular relationships and directions from a given central point use this projection. Maps for aeronautical purposes use this principle. The Lambert Azimuthal Equal-Area projection and the Gnomonic projection are examples of how azimuthal projection is used for map making.
There are some maps that combine all the above mentioned principles or use a compromise between them to depict the world and countries.
For example, Robinson projection that showed the entire world at a glance can be said to be a compromise between the equal-area and conformal map projection. The objective behind its creation was to show the entire globe as a flat image. However, the Robinson projection was replaced later by the more modified version called the Winkel tripel projection, which is considered to be a blend of the azimuthal Aitoff projection and the equirectangular projection.
At present, digital maps use either one or more than one of these aforesaid map projection types to create interactive maps that not only show the data in a much reliable way but also let the users utilize the maps to get additional information based on add-on clickable icons, pushpins, tool tip or mouse over info boxes etc.
If you still haven't enjoyed the use of digital flash maps with several user friendly, interactive features, it's time to shift from the traditional paper maps to see the sales graphs soar.
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