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3.4.1 Introduction

This chapter deals with projection transformations. See a diagram explaining various coordinate transformations to see how projections fit into the scheme.

A projected coordinate system is the result of the application to a geographic coordinate system of a coordinate transformation using a projection method and a set of parameters specific to that method

Setting aside the large number of projections which may be employed for atlas maps, equally small scale illustrative exploration maps, and wall maps of the world or continental areas, Epicentre provides reference entities for only those orthomorphic or conformal projections which are used for medium or large scale topographic or exploration mapping. Here accurate positions are important and sometimes users may wish to scale accurate positions, distances or areas from the maps.

Small scale maps normally assume a spherical earth and the inaccuracies inherent in this assumption are of no consequence at the usual scale of these maps. For medium and large scale sheet maps, or maps and projected coordinates held digitally to a high accuracy, it is essential that due regard is paid to the actual shape of the earth. Such maps are therefore invariably based on an ellipsoid and its derived projections. Epicentre, through the considers only projected coordinate systems for the ellipsoid.

Though not exhaustive the following list of named projection methods are those which are most frequently encountered for medium and large scale mapping, some of them much less frequently than others since they are designed to serve only one particular country. They are grouped according to their possession of similar properties, which will be explained later. Except where indicated all are conformal.

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