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* Projections A map projection is used to portray all or part of the round Earth on a flat surface . This cannot be done without some distortion . Every projection has its own set of advantages and disadvantages . There is no "best" projection . GIS users must select the projection best suited ` to specific organization (or peojecf) needs, reducing distortion of the most important features . Map projections can be grouped together in two basic ways ; and a third characteristic , although if divides different way of using the same projection , is sometimes considered important enough that different versions of the same projection varying only in this characteristic are given different names . The first characteristic is aspect. This identifies the basic layout of the projection . The most important projections are either cylindrical , conic , or azimuthal . A flat piece of paper can , without stretching , be bent into a cone or a cylinder, and in this way, it can touch a globe along an extended line : if left flat, it only touches the globe at a point . The basic mathematics of obtaining several important properties of maps is different in these aspects . Projections are also classified in terms of their properties . Specifically , on the basis of two very important properties : whether they are conformal , or equal-area . A conformal projection maintains the shape of small regions, so angles at any point are correct, although sizes will change . An equal-area projection , on the other hand, maintains size of the expense of shape . Maintaining both size and shape , of course , requires a globe . In general , and this is true for the projections in the three basic aspects of cylindrical , conic , and azimuthal , scale going away from the center of a map increases for a conformal projection , and decreases for an equal-area projection . Most projections that are neither conformal nor equal area have a scale behavior that is somewhere in between . However, two very important azimuthal projections lie outside this range : the gnomonic projection , which can be used to find the great circle path between two places, and whose scale expands more quickly than that of a conformal projection , and the orthographic projection , which looks like a picture of a globe , whose scale shrinks more quickly than that of an equal- area projection . Finally, there is the case of a projection . In essence , the lines of latitude and longitude (graticules ) on the globe can be moved . Thus by shifting a graticule on the globe , one can draw a map of a shifted world : that is , although the usual rules for drawing a projection place the lines of latitude and longitude on it in a given way, one can shift the world under the projection 's graticule , and treat the original graticule of the world like the coastlines and borders on the globe, as simply things to be drawn where they happen to be . There is the conventional (or, in the case of an azimuthal projection , polar) case , where the projection is drawn in the normal and easiest fashion . There is the transverse ( or, in the case ' of an azimuthal projection , equatorial ) case , in which the globe has been shifted by 90 degrees before the map is drawn , and there is the oblique case where the globe is shifted by a lesser amount . ' 6-S GIS Needs Assessment and Implementation Plan Chapter 6 - Data Standards and Transfer