How to make a flat Earth

THE United States space shuttle Atlantis, with its German satellite-borne experiments, returned to Earth this week with 180 hours of remote-sensing data on the ozone hole over Antarctica. The first understandable product of the data that most of us will see will be a kind of map: probably a composite of false-color imagery, manipulated to correspond to a sensible view of our globe.

There's more to geography than maps, yet because our world is a vast physical thing, with features and properties that can be counted and measured, it's often useful to make a visual picture of it. Maps hold a central place in understanding the planet.

Scientist's instruments now reach farther into space, deeper into the ocean and the Earth's crust, and perform complex calculations faster than ever. But before we leap farther into the future, this could be a good time to take a back-to-basics look at what mapmakers do, and how trends in world mapmaking figure in our lives.

PROJECTIONS

This is the mapmaker's assignment: Convert the spherical surface of our globe to a flat drawing.

If you picture someone peeling an apple and trying to flatten the peels onto a countertop, you'll see the problem: The edges of the peels split, the curled ends don't match up, and the pieces from the top and bottom (the ``poles'') are too curly to do anything with. In addition, if your goal is to represent the ``whole apple,'' you have to make some decisions. Which arrangement of the peel is a more faithful view of the apple's surface?

Choosing what to distort and what to keep accurate

Cartographers must make such choices all the time in mapping the Earth. And they solve the problem in myriad distinct ways. A choice may depend on the use for which the map is intended; ``aesthetic'' judgment; cultural bias; and practical concerns such as budget or printing requirements.

(``Local'' curvature -- hills and valleys -- is more important to large-scale maps than projection, and is crucial to hikers, road-builders, airplane pilots, and others. That is why large-scale maps such as geologic survey maps show contour lines, one method of depicting three-dimensional landforms.) Mercator

The Mercator projection is 400 years old and has been one of the mainstays of general atlases this century. Originally developed for oceangoing navigation, its strength is that compass bearings are true and straight anywhere on the globe.

Another strength of the Mercator is that it is ``conformal''; that is, within smaller regions (say, Australia) local landforms agree with their true shape on the globe. But comparing landforms at different latitudes is not recommended -- for example, Alaska appears to be about three times larger than Mexico, when in reality Mexico is 16 percent larger.

Peters

Arno Peters's equal-area projection, introduced in the 1960s, sought to correct the drawbacks of the Mercator, especially when used to display quantitative data such as population, wealth, health, or natural resources. The Peters is one of a number of projections that sacrifice shape in favor of area.

In this view, Africa takes center-stage as more dominant by far than Europe, as indeed it is. Little wonder that this ``politically correct'' projection was early adopted by developing-world charities and certain United Nations agencies.

The Peters projection also pushed cartography into the limelight when established cartographic agencies resisted the new projection. Some experts noted that the Peters projection's awkwardness lies in its unfamiliarity, and that the Mercator's equally untrue distortions earned their ring of correctness in an era when colonial seafaring nations ruled the globe. Robinson

The Robinson is a sort of compromise projection -- neither conformal (accurate shapes) nor equal-area -- but relatively near to both and well-respected as a useful general-reference view. Many of the continental and world maps that accompany news articles in the Monitor use the Robinson projection -- at least in part because it has become so widely used in the atlases and mapping services we refer to.

Monitor thematic maps, which compare regions of the globe with colored keys, are usually drawn on equal-area projections, sometimes the Peters. Other projections

The number of possible projections is infinite. Fine atlases will always tell the reader which projection is being used. They have names such as Azimuthal Equidistant, Lambert Conformal Conic, Polyconic, and Polar Stereographic. As we learn more about reading maps, we become more critical of the strengths and weaknesses of each world view, and more careful of conclusions we may draw from them.

THE STATE OF THE ART

The use of computers has greatly expanded the variety of maps available to students, professionals, and the public, and given new tools to cartographers.

Hammond Inc. recently published a complete line of ``revolutionary computer-generated atlases.'' The company's efforts illustrate three areas where computers have been helpful:

1. Database development: Rapid political change around the world this decade presented a new generation of cartographers with an age-old challenge: how to keep atlases accurate. Now detailed world maps that took months or years to draw and redraw can be updated in less than half the time.

2. Topographic rendering: The Hammond maps in particular illustrate hills and mountains with striking realism. This has been achieved in part with sophisticated fractal-based programming.

3. ``Optimal'' conformal projections: Again using powerful computer algorithms, cartographers are creating new projections that present ever-more ideal compromises between fidelity to area and shape. These are useful for continent-sized areas. Databases/CD-ROM

Cartographers caution that erroneous base maps can ``contaminate'' many more maps today, through proliferation in any map generated from them. At the Monitor we constantly watch that an outdated map of, say, Eastern Europe, doesn't get used from our large digital database.

Database map publishing has expanded beyond business use of geographic information systems (GIS) to home and traveler use, through CD-ROM for home computers. Check these products out as you would an atlas: Zero in on a part of the world you know well, to get a sense of its completeness and fidelity. Animated maps

Digital video and interactivity on the global information superhighway are creating new mapping opportunities. Some media pioneers are experimenting with animated maps that run like miniature movies on a computer screen to show physical changes, economic activity, or news events on the Earth.

Most important, each could include a spinning globe, reinforcing the spherical nature of the Earth and helping to solve (in the mind's eye) the mapmaker's primal challenge. Text and graphics by John Van Pelt

You can respond to this article by sending e-mail on the Internet to: jvanpelt@world.std.com.

National Geography Awareness Week, sponsored in part by the National Geographic Society, is being observed in the US Nov. 13-19.