Zambia is one of Sub-Saharan Africa's most highly urbanized countries. The mining of copper dominates Zambia's national economy. The mining sector is the backbone of the economy and the major source of foreign exchange earnings. The country possesses 6% of the worlds copper reserves. Apart from copper mining and processing, construction, foodstuffs, beverages, chemicals, textiles, fertilizer and horticulture are also notable industries in the country. Copper, cobalt, electricity, tobacco, flowers, and cotton are the main exports. The principal imports are machinery, transportation equipment, petroleum products, electricity, fertilizer, foodstuffs, and clothing. The leading trade partners are South Africa, Switzerland, and Great Britain.