Center for Modeling & Simulation

► A means of converting coordinates on a curved surface to coordinates on a plane ► The surface of projection can be a plane, a cylinder, or a cone, than can be unfolded (perspective projection) ► This can be modified so that certain properties can be maintained such as equal area, equal distance, or correct shape (non-perspective)

► Map projections vs. coordinate systems - Map projections define how positions on the earth’s curved surface are transformed onto a flat map surface - Coordinate systems is used to specify the location of the feature in 2-3 dimensional space

Earth can be considered as an orange as a perfect sphere When you represent the earth on the flat surface some of the properties will be lost like Area Shape Distance Direction Once the earth is transformed into a plane only some of these properties can be maintained Thus all the different projections maintain one or two of these properties in the final map for specific purpose

 The area measured on the map is the same as that measured on the earth  It is called as equal area or equivalent projection

 IT distorts the shape of the graticule  Used to show spatial distributions and relative sizes of features like, political units, population, landuse landcover wildlife habitats etc  The size of the real world features is visually compared on the same areal basis  However, shape, distance and at times directions are distorted

 Map projection maintains the correct shape of the spatial features  Called as conformal or orthmorphic  Angles remain same as measured on the earth’s surface  Meridians intersect parallels at right angles  Both area and distance get distorted  Used for topographic mapping and navigation

 The distance measured between the two points on the map is equal to that between the same two points measured on earth’s surface and scaled  This is possible along only by selecting certain lines along which the scale remains true  Thus distance can be measured correctly in only one direction  This type of projection is called as equidistant  It is very sensitive to scale change  Shape and area are distorted  Generally used in atlas maps

 Direction measurements remain same  It is an inherent property of azimuthal map projections  However, they are accurate for only one or two selected points  It is useful for air and sea navigation charts

 A classification of map projections  By conceptual methods Cylindrical, Azimuthal, and Conic  By distortions Conformal, Equal-area, Equidistant, and Azimuthal

cylinder that has its entire circumference tangent to the Earth’s surface along a great circle (e.g. equator)

 A cone is places in such way that the cone is exactly over the polar axis  It must touch the globe along a parallel latitude known as the standard parallel  Scale is correct and distortion is least along this  When the cone is cut along this a fan shaped map is produced

 projecting positions directly to a plane tangent to the Earth’s surface  It is circular in shape with meridians projected as straight lines radiating from the centre of the circle  The parallels are complete circles centered at the pole

 map purpose  for distribution maps: equal area  for navigation: projections that show azimuths or angles properly  size of area some projections are better suited for East-West extent, others for North-South for small areas the projection is relatively unimportant for large areas the projection is very important

 Conic projections for mid-latitudes  true along some parallel between the poles and equator  Cylindrical for equatorial regions  true at the equator and distortion increases towards the poles  Azimuthal for poles  true only at their center point but distortion is generally worst at the edges

 Establishing a spatial framework for mapping locations on earth  Defined as the representation of the location of real world features within the spatial framework of a particular coordinate system  Objective is to provide a rigid spatial framework in which positions of real world are computed, recorded and analyzed  Practically it is series of techniques that transforms the measurements of irregular surface of the earth to the map by means of a coordinate system