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1.3 Principles of Cartography – ’s ‘ qu Wo ld’!
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Figure 14: Shows the hierarchy of mapping.
The foundation is the datum. Geographic coordinates (latitude and longitude) describe points in the datum. These are then converted into Projection coordinates.
Without knowledge of the datum, projection coordinates are not unique and can easily be wrongly mapped.
Why is it necessary to project geographic coordinates? We do this for three primary reasons:
Ease of communication Ease of computation Presentation and Planning
• • •
1.3.1 Projection Categories Figure 14 shows the various surfaces and orientation of the surfaces with respect to the ellipsoid axes. The three surfaces for projecting the ellipsoid are a cylinder, a cone and a plane. The main projection types used in E&P are Transverse Mercator and Lambert Conformal Conic . Other projection types that occur less frequently are: Mercator, Oblique Mercator (Alaska) Oblique Stereographic (Syria), Albers Equal Area . The majority of the standard projections in use in E&P are listed with parameters in the EPSG database.
h m ny ‘s nd d’ poj c on parameter definitions, but a project projection can be custom designed for specific purposes if needed. In general, one or two of the following criteria can be preserved when designing a projection:
Shape Area Scale Azimuth
The majority of the projections we use are conformal. This means that scale at a point is the same in all directions, angular relationships are preserved (but not necessarily north reference) and small shapes and areas are preserved.
Figure 15: Shows the various types of projection based on various plane surfaces and the orientation of the surface with respect to the ellipsoid.
They are also generally computational.
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