Jeffrey S. Dumele, age 8, of Niagara Falls, Ontario, Canada, for his question:

What is a Mercator Projection?

Gerhardus Mercator lived in Belgium, way back in the 1500s. He was an expert in geography and the best map maker of his day. He invented the word "atlas" as well as a way to make maps more helpful to travelers. The sailors, of course, used compasses to check their directions. They also used the lines of latitude and longitude to chart their voyages. Mercator marked these lines right on his famous maps. They showed a gridwork of squares so that travelers could figure the latitude and longitude of places along the way.

This helpful invention is called the Mercator Projection. Many pilots still like it and use it. But the squares do not give a true picture of our curving globe. Actually, the lines of longitude taper together and meet at the poles. Mercator drew them as straight up and down lines. His projection stretches the polar longitudes apart. On a world map, this makes the polar regions look wider than they really are. But the Mercator Projection is still fine for plotting short journeys and even for certain long journeys.