Geoffrey Vincent, age 11, of Dorval, Quebec, Canada, for his question:

Which is the largest city in Africa?

The huge continent of Africa is home to more than 350 million persons    and almost one tenth of them live in Egypt. Throughout the continent, the average population density is 30 people to the square mile. But Egypt tops this figure with an average density of 1,000 people per square mile. Most of its people farm the rich land, though the country has more than its share of sizeable and very ancient cities. Its capital city of Cairo has an estimated population of 3,518,000    which rates it among the major cities of the world. Cairo is Africa's largest city and home to about one per cent of all the people on the continent.

Africa has several cities with populations between 500,000 and two million. Most of them are seaports. Casablanca and Algiers, Tunis and Alexandria are along the Mediterranean. Durban and Capetown are on the far southern shores, way below the equator.