OrthographicPlate CarreeAll circles are same shape and areaShape distortionNotice stretching of meridians so that they can be shown as straight lines.
Azimuthal equidistantPreserves distance and direction pasting through one point
RobinsonPreserves a bit of everything
ESRI Virtual Campus, ‘Referencing Data to Real Locations’Developable surface –surface that can be laid flat without any stretching or tearingPlaneCylinderConePolar maps in normal (polar) aspectWorld maps in normal (equatorial) aspectContinental maps mid-latitude in normal (polar) aspectProjection surfaces
Projection surfacesESRI Virtual Campus, ‘Referencing Data to Real Locations’Tangent –surface touches sphereSecant –surface cuts through sphereNo distortion at contact pointsDistortion increases away from contact points
Which projection to use?
Projection ParametersWhen we define a projection on a map we need to understand the various parameters that are required:•Units•Scale•Scale factor•Standard parallels / latitudes•Origin•False easting/northing•Ellipsoid•Datum
Projection Parameters•Units•The unit of measure used for map coordinates•e.g., meters, feet, decimal degrees (DD)•Many projections (e.g., UTM, Transverse Mercator) are defined for meters only•Scale•Represents the ratio of a distance on the map to the same distance on the earth e.g., 1:50,000. •But:it is not possible to transform a spherical surface to a plane without stretching or shrinking parts of the map and therefore this scale is not constanteverywhere•Thus, most projections have one or two lines where scale is constant. The map scale at these locations is known as the "principal scale" or "true scale".