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