Conical Projections

Four well-known normal conical projections are the Lambert conformal conic projection, the simple conic projection, the Albers equal-area projection and the Polyconic projection. They give useful maps of mid-latitudes for countries which have no great extent in latitude.

1.Lambert conformal conic projection:

The Lambert conformal conic projection is confomal. The parallels and meridians intersect at right angles (as in any conformal projection). Areas are, of course, inaccurate in conformal projections. Like with other conformal projections, Lambert’s conical is also widely used for topographic maps. It is adapted in France and recommended to the European Commission for conformal pan-European mapping at scales smaller or equal to 1:500,000.

Lambert Conformal Conic projection (standard parallels 10 and 30 degrees North).

2.Simple conic projection:

The simple conic projection (figure below) is a normal conical projection with one standard parallel. All circular parallels are spaced evenly along the meridians, which creates a true scale along all meridians (i.e. no distortion in north-south direction). The map is therefore equidistant along the meridians. Both shape and area are reasonably well preserved. Whereas small countries are possibly shown on this projection, larger areas, such as Russia or Europe are better portrayed on the conic projection with two standard parallels.

Simple conic (or equidistant conic) projection (standard parallel 15 degrees North). The meridians are true to scale.

3.Albers equal-area projection:

The Albers equal-area projection uses two standard parallels. It represents areas correctly and has reasonable shape distortions in the region between the standard parallels as compared with the noticeable distortions of the Lambert’s equal-area conic projection with one standard parallel. This projection is best suited for regions predominantly east-west in extent and located in the middle latitudes. Used for small regions or countries but not for continents. It is adapted for maps of the United States, for thematic maps and for world atlases.

Albers equal-area conic projection (standard parallels 10 and 30 degrees North).

5.Polyconic projection:

The polyconic projection is neither conformal nor equal-area. The projection is a derivation from the simple conic projection, but with every parallel true to scale (similar to the Bonne’s equal-area projection). The polyconic projection is projected onto cones tangent to each parallel, so the meridians are curved, not straight (figure below). The scale is true along the central meridian and along each parallel. The distortion increase rapidly away from the central meridian. This disadvantage makes the projection unsuitable for large areas on a single sheet. It is adaptable for topographic maps, and is earlier used for the International Map of the World, a map series at 1:1,000,000 scale published by a number of countries to common internationally agreed specifications, and also for large-scale mapping of the United States until the 1950’s and coastal charts by the U.S. Coast and Geodetic Survey.

Polyconic projection, with true scale along each parallel.

6.Pseudo-conical projections:

Pseudo-conical projections are projections in which the meridians are represented by curves, and the parallels are equally spaced concentric circular arcs (unlike the pseudo-cylindrical projections in which the parallels are represented by straight lines). The central meridian is the only meridian that is straight. Examples are the Bonne and Werner projection.

Bonne’s projection (figure below) is a pseudo-conical equal-area projection, with every parallel true to scale (similar to the polyconic projection). The projection was once popular for large-scale topographic maps and to map the different continents. The Werner projection is a variant of Bonne’s projection with the standard parallel at the North or South pole.

Bonne’s projection (standard parallel 60 degrees North), with true scale along each parallel.




About Rashid Faridi

I am Rashid Aziz Faridi ,Writer, Teacher and a Voracious Reader.
This entry was posted in Class Notes, earth, Geography Practicals/Lab and Statistical Techniques. Bookmark the permalink.

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