232 Modern Business Geography Khartum form the only important centers on the upper Nile above the famous cataracts. The other great rivers are blocked by cataracts nearer the sea than those of the Nile, and consequently do not furnish routes of transportation of much importance. 35. Does this fact lead you to expect many or few large cities in the interior of Africa? Why? Compare Africa with South America with respect to interior centers. How does the largest river of Africa compare with the largest river of South America as a means of transportation ? 37. Where in Africa does the climate most favor the growth of cities? 38. How many of the interior cities in the table on page 228 are located out~ side of the tropics? How far from the coast are they? To. 158. Taking clav pots down the Nile to market.