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Mapping our Globe - Choosing an Equal-Area Map
If the vital decision to use an 'equal-area' world has been made, the next question is, which equal-area map is best? All equal-area maps distort shapes - some far more than others. Students could evaluate various maps by comparison with the globe or compare the shapes on these maps with the 'segment and three sectors' diagram: each map can be judged against this. Judge at the edges as well as at the centre - on most maps the edges are where the distortion is greatest.
Often-used equal-area maps include Eckert IV, Peters, Mollweide, Hammer, and Sanson-Flamsteed - all named after their originators. An alternative is to go for an interrupted equal-area map.
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This map has received much publicity in recent years. Unfortunately many people have wrongly assumed that the Peters projection is the only equal-area world map.
Peters does deserve credit for pressing the case for 'equal-area' world maps, but his map has huge distortions of shape. Pupils can identify these distortions if they are invited to compare this map with the accurate globe. For example, his Africa looks as long and thin as South America really is.
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Some of the claims Peters made for his map are simply wrong, and his rhetoric ignores the other equal-area map projections. An expert evaluation of the Peters map concluded (among several other damning statements):
'The Peters Map conveys a distorted view of the world. Developing countries near the equator are totally deformed. The Peters map is totally unsuitable to represent the countries of the Third World.' (Pape, H. et al, 'The So-called Peters Projection', Cartographic Journal, Vol. 22, Dec. 1985)
Despite this wholesale condemnation, the Peters map continues to be popular with people who do not compare it with the globe (for example some aid agencies) and who do not realise that there are other equal-area maps available.
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Eckert IV lay in well-deserved obscurity for many years. It was then the surprise choice for the 1995 revision of the National Curriculum. Eckert IV is also too 'long and thin' in the tropics. The distortion is not as extreme as Peters, but Africa still looks too much like Latin America, which could confuse some children. Even Mr Eckert himself did not like this projection much, he preferred his Eckert VI.
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| Mollweide, Sanson-Flamsteed and Hammer |
These projections can be summed up as 'good at the centre, too distorted at the extremes'. This is clear from comparison with our 'sector and segments' diagram. They are, however, arguably better than Eckert IV in that the 'bending' is obvious - the 'stretching' in Eckert IV is not so obvious. But ask pupils what New Zealanders might think of these map projections. If they are centred on the Greenwich Meridian the answers may be unprintable...
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| Mollweide, Sanson-Flamsteed and Hammer |
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| Interrupted map projections |
An 'interrupted' equal-area map is arguably the ideal solution to the problem of the 'round world on flat paper' problem. By making cuts in the oceans, these maps are the nearest one can get to a flat map that is correct in size and also correct in shape. They are the most similar to our 'sector' approach - they should be used much more. Children have no major conceptual problems in handling such maps once they have 'unpeeled the orange' and seen why there are gaps.
In fact, interrupted maps can help to clarify an important point: every world map is already cut at the edges. All we are doing is adding a few more cuts. There is a strong case for recommending the use of interrupted equal-area maps.
An objection that is sometimes made about interrupted world maps is that it is hard to measure long distances accurately on this type of map. True - but this is also true for almost all world maps. Most of these measurements inevitably produce wrong answers. It is far better to use a globe.
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| Where should the cuts be made? |
This is a worthwhile discussion point that can involve pupils as well as teachers. Make sure that cuts means rips or tears, not deletions.
(a) Greenwich-centred - the most common choice is to have a map centred near to the Greenwich Meridian, with the edge-cut through the Pacific (180º) and three smaller cuts through the North Atlantic, South Atlantic and Indian Oceans.
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| Interrupted Mollweide (Greenwich-centred) |
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(b) Extra cuts - that 'top choice' leaves East Asia distorted. Sometimes an extra cut is made in remote Siberia, to compensate for this. Or an extra cut can be made in the Pacific.
(c) Americas-centred - it cuts Asia in half, but perhaps helps us to understand how Americans see the world?
(d) Pacific-centred - this is rare, but not impossible. Fiji issued a postage stamp that put itself in the centre of the world on such a projection!
(e) North Pole centred - this produces an exciting and effective star-shaped world map. There is no right way up. It might be seen as an improvement on the UN flag. But, in practice, it is rarely seen.
(f) South Pole centred - an idea to puzzle your students - what would it look like?
(g) Cuts in the land-masses instead of the oceans? - these maps are rare - but they are useful for showing ocean currents, and for emphasising that over 70% of the earth's surface is water.
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The detailed decision over which interrupted world map is best is less important than the decision to use maps of this type. Interrupted Mollweide is popular, Interrupted Sanson-Flamsteed produces points instead of curves at the poles, which may seem more pleasing shapes. The Goode map is similar, and is used in some textbooks. The (W)right World Map created by the author of this text, David R Wright, is another choice. (Please note that the map is © 2007, but you are welcome to use it for non-profit educational activities, and it is available free for certain charities, on request.)
Download: (W)right World Map (PDF)
Download: (W)right World Map - Explanation (Word)
Download: (W)right World Map - Q & A (Word)
The main message remains that interrupted maps are really useful in studying world geography.
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A PDF template of the Eckert IV projection, recommended in the National Curriculum, is available to download below:
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