Mercator and the Australian Map Grid

Five hundred years ago Gerhard Mercator was born on the 5 March 1512 in Rupelmonde in the Hapsburg County of Flanders, Holy Roman Empire (he died 2 December 1594 in Duisburg, United Duchies of Jülich-Cleves-Berg, Holy Roman Empire). Named Gerard de Gemor or de Cremer by his parents from Gangelt in the Duchy of Jülich where he was raised, "Mercator" is the Latinised form of his name; it means "merchant". He was educated in 's-Hertogenbosch by the famous humanist Macropedius and at the University of Leuven.

Gerhard Mercator	Museum of the History of Science, Oxford U.K.
Engraving by Frans Hogenberg	Renaissance in astronomy panel-Gerard Mercator

While Mercator is best known as a cartographer, his main source of income came through his craftsmanship of mathematical instruments. In Leuven, he worked with Gemma Frisius and Gaspar Myrica from 1535 to 1536 to construct a terrestrial globe, although the role of Mercator in the project was not primarily as a cartographer, but rather as a highly skilled engraver of brass plates. Mercator's own independent map-making began only when he produced a map of Palestine in 1537; this map was followed by another - a map of the world (1538) – and a map of Flanders (1540). During this period he learned Italic script because it was the most suitable type of script for copper engraving of maps.

In 1552, he moved to Duisburg, one of the major cities in the Duchy of Cleves, and opened a cartographic workshop where he completed a six-panel map of Europe in 1554. He worked also as a surveyor for the city and taught mathematics at the academic college of Duisburg. After producing several maps, he was appointed Court Cosmographer to Wilhelm, Duke of Jülich-Cleves-Berg in 1564. He constructed a new chart and first used it in 1569. It had parallel lines of longitude to aid navigation by sea, and compass courses could be marked as straight lines.

Mercator’s name lives on in that famous conformal world map projection, which has been used by navigators for the last five centuries.

The international cartographic community celebrated Mercator’s 500^th anniversary in April 2012 by supporting a conference which took place in his native Flanders (in the City Hall of Sint-Niklaas, just 10 kilometres from his birthplace, where a Mercator exhibition was also presented). This meeting highlighted Mercator’s work (his training, resources and the mathematics, science and technology of his craft), his context (the impact of the Age of Discovery on cartography, the world view and philosophy of Mercator’s time) and his legacy (particularly contemporary approaches to cartographic heritage and application of new techniques to the handling of data and products from Mercator’s era). Mercator’s less well-known work including that on the Earth’s magnetism, the design of italic text for atlas map engraving, and the toponymy of Balkan areas was also in the programme.

Walachia, Servia, Bulgaria, Romania, published in Amsterdam, 1630 by MERCATOR.

Five hundred years on, we should also recognise that the basis for Australian topographic mapping, the Australian Map Grid (AMG), is historically based on Mercator’s work.

As mentioned above the feature of a Mercator map is that any straight line on the map is a loxodrome or rhumb line. Thus for navigation one only needs a compass to get from point to point. The Equator and other parallels are straight lines (their spacing increasing toward the poles) and meet meridians (equally spaced straight lines) at right angles. Distances are true only along the Equator, but are reasonably correct within 15° of the Equator. Areas and shapes of large areas are distorted and distortion increases away from the Equator and is extreme in polar regions. The Mercator map, however, is conformal in that angles and shapes within any small area are acceptable. Refer Figure 1. Mathematically the Mercator projection is described as being Cylindrical whereby positions on the earth are projected onto a cylinder tangent to the Equator.

Figure 1 : Features of the Mercator projection.

While useful for navigation, for mapping especially away from the Equator and the portrayal of the earth with less distortion, the Mercator projection had its limitations.

Figure 2 : Features of the Transverse Mercator projection.

In 1772 the Transverse Mercator was revealed. While mathematically still a Cylindrical projection the positions on the earth are projected onto a cylinder tangent to a meridian. Refer Figure 2. Now distances are true only along the central meridian selected by the mapmaker or else along two lines parallel to it, but all distances, directions, shapes, and areas are reasonably accurate within 15° of the central meridian. Distortion of distances, directions, and size of areas increases rapidly outside the 15° band. Because the map is conformal, however, shapes and angles within any small area are essentially true. The Equator is straight line with other parallels complex curves concave toward nearest pole. The Central meridian and each meridian 90° from it are straight. Other meridians are complex curves concave toward central meridian. By selecting central meridians at suitable intervals and keeping well within the ±15° limitation each side of the selected central meridians, large areas can be mapped with minimal distortion.

Initial topographic mapping in Australia was based on the British Modified Grid and its underlying Polyconic projection; great for displaying a north-south oriented landmass like England but totally inadequate in Australia’s case. In 1936 a transverse Mercator projection was adopted which covered the whole of Australia in 8 zones. Each zone was 5 degrees of longitude wide with a half degree of common overlap. This was a simple projection with no provision for a scale factor and with each zone’s ‘true origin’ at 34 degrees south latitude. This projection was used for the R502 1:250,000 scale map series covering Australia.

After the Second World War, a world-wide map projection system was adopted, the Universal Transverse Mercator (UTM). The UTM system divided the earth into 60 zones each 6 degrees of longitude wide. These zones define the reference point for UTM grid coordinates within the zone. UTM zones extend from latitude 80° S to 84° N. In the polar regions the Universal Polar Stereographic (UPS) grid system is used. UTM zones are numbered 1 through 60, starting at the international date line, longitude 180°, and proceeding east. Zone 1 extends from 180° W to 174° W and is centred on 177° W.

The Australian Map Grid (AMG) when adopted in 1966 accepted the UTM as its underlying projection system. Australian territory falls within Zones 49 to 57 inclusive, of the UTM.

A number of the R502 1:250,000 scale map series were overprinted (in cyan) with the AMG but for the later NTMS 1:250,000 and 1:100,000 scale series the AMG was standard.

Even today just about any medium scale topographic map is highly likely to have the word “Mercator” somewhere in the legend, such is Mercator’s legacy.

For more on map projections or the AMG the following references are a good starting point.

Paul Wise, August 2012

References

Intergovernmental Committee on Surveying and Mapping (ICSM), Australia http://www.icsm.gov.au/mapping/map_projections.html accessed August 2012.

Lines, J. D. (1992) Australia on Paper – The Story of Australian Mapping, Fortune Publications, Box Hill.

United States Geological Survey (USGS) http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html accessed August 2012.