Question: What type of vegetation is in the central area of the country with the largest economy in Africa?

full_context: Document 1: Nigeria: As of 2015[update], Nigeria is the world's 20th largest economy, worth more than $500 billion and $1 trillion in terms of nominal GDP and purchasing power parity respectively. It overtook South Africa to become Africa's largest economy in 2014. Also, the debt-to-GDP ratio is only 11 percent, which is 8 percent below the 2012 ratio. Nigeria is considered to be an emerging market by the World Bank; It has been identified as a regional power on the African continent, a middle power in international affairs, and has also been identified as an emerging global power. Nigeria is a member of the MINT group of countries, which are widely seen as the globe's next "BRIC-like" economies. It is also listed among the "Next Eleven" economies set to become among the biggest in the world. Nigeria is a founding member of the Commonwealth of Nations, the African Union, OPEC, and the United Nations amongst other international organisations.
Document 2: Nigeria: Nigeria was ranked 30th in the world in terms of GDP (PPP) in 2012. Nigeria is the United States' largest trading partner in sub-Saharan Africa and supplies a fifth of its oil (11% of oil imports). It has the seventh-largest trade surplus with the US of any country worldwide. Nigeria is the 50th-largest export market for US goods and the 14th-largest exporter of goods to the US. The United States is the country's largest foreign investor. The International Monetary Fund (IMF) projected economic growth of 9% in 2008 and 8.3% in 2009. The IMF further projects an 8% growth in the Nigerian economy in 2011.
Document 3: List of African countries by GDP (nominal): 2017 Rank Country Nominal GDP ($billions) Nominal GDP per capita (US $) Notes Nigeria 376.284 1,994.235 South Africa 349.299 6,179.870 Egypt 237.037 2,500.772 Algeria 178.287 4,292.272 Angola 124.209 4,407.657 6 Sudan 119.00 1,428.000 7 Morocco 109.824 3,151.145 8 Ethiopia 80.874 872.840 9 Kenya 79.511 1,701.550 10 Tanzania 51.725 1,033.567 11 Ghana 47.032 1,663.190 12 Democratic Republic of the Congo 41.441 478.237 13 Ivory Coast 40.360 1,616.981 14 Tunisia 40.275 3,496.286 15 Cameroon 34.006 1,400.743 16 Libya 31.331 4,858.672 17 Uganda 26.349 699.410 18 Zambia 25.504 1,479.542 19 Zimbabwe 17.491 1,175.723 20 Botswana 17.168 7,876.997 21 Senegal 16.463 1,038.094 22 Mali 15.318 810.771 23 Gabon 15.206 7,971.589 24 Namibia 12.687 5,413.508 25 Mozambique 12.681 429.296 26 Burkina Faso 12.569 663.806 27 Mauritius 12.428 9,794.102 28 Madagascar 11.463 447.558 29 Equatorial Guinea 10.725 12,726.956 30 Chad 9.872 810.163 31 Guinea 9.721 749.463 32 Benin 9.238 830.404 33 Rwanda 9.137 771.702 34 Congo 8.513 1,958.174 35 Niger 8.253 439.997 36 Somalia 7.382 547.32 37 Malawi 6.206 323.740 38 Eritrea 5.813 979.692 39 Mauritania 5.116 1,317.938 40 Togo 4.767 611.133 41 Swaziland 4.491 3,914.821 42 Sierra Leone 3.641 491.448 43 Burundi 3.396 312.463 44 Liberia 3.285 729.292 45 South Sudan 2.870 228.034 46 Lesotho 2.768 1,425.310 47 Djibouti 2.029 1,988.765 48 Central African Republic 1.928 386.806 49 Cape Verde 1.741 3,237.597 50 Seychelles 1.482 15,685.955 51 Guinea - Bissau 1.350 794.107 52 The Gambia 1.009 480.040 53 Comoros 0.652 787.831 54 São Tomé and Príncipe 0.379 1,785.280 -- Total 2,191.104
Document 4: Chad: Chad has several regions: a desert zone in the north, an arid Sahelian belt in the centre and a more fertile Sudanian Savanna zone in the south. Lake Chad, after which the country is named, is the largest wetland in Chad and the second - largest in Africa. The capital N'Djamena is the largest city.
Document 5: Sahara: The desert comprises much of North Africa, excluding the fertile region on the Mediterranean Sea coast, the Atlas Mountains of the Maghreb, and the Nile Valley in Egypt and Sudan. It stretches from the Red Sea in the east and the Mediterranean in the north to the Atlantic Ocean in the west, where the landscape gradually changes from desert to coastal plains. To the south, it is bounded by the Sahel, a belt of semi-arid tropical savanna around the Niger River valley and the Sudan Region of Sub-Saharan Africa.
Document 6: Nigeria: Everything in between the far south and the far north is savannah (insignificant tree cover, with grasses and flowers located between trees). Rainfall is more limited, to between 500 and 1,500 millimetres (20 and 60 in) per year. The savannah zone's three categories are Guinean forest-savanna mosaic, Sudan savannah, and Sahel savannah. Guinean forest-savanna mosaic is plains of tall grass interrupted by trees. Sudan savannah is similar but with shorter grasses and shorter trees. Sahel savannah consists of patches of grass and sand, found in the northeast. In the Sahel region, rain is less than 500 millimetres (20 in) per year and the Sahara Desert is encroaching. In the dry north-east corner of the country lies Lake Chad, which Nigeria shares with Niger, Chad and Cameroon.
Document 7: Nigeria: Nigeria is often referred to as the "Giant of Africa", owing to its large population and economy. With approximately 182 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has one of the largest populations of youth in the world. The country is viewed as a multinational state, as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages, and are identified with wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims in the northern part. A minority of the population practise religions indigenous to Nigeria, such as those native to Igbo and Yoruba peoples.
Document 8: Sahara: To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the southern limit of the Sahara corresponds to the 150 mm (5.9 in) isohyet of annual precipitation (this is a long-term average, since precipitation varies annually).
Document 9: Namibia: Namibia is the driest country in sub-Saharan Africa and depends largely on groundwater. With an average rainfall of about 350 mm per annum, the highest rainfall occurs in the Caprivi in the northeast (about 600 mm per annum) and decreases in a westerly and southwesterly direction to as little as 50 mm and less per annum at the coast. The only perennial rivers are found on the national borders with South Africa, Angola, Zambia, and the short border with Botswana in the Caprivi. In the interior of the country surface water is available only in the summer months when rivers are in flood after exceptional rainfalls. Otherwise, surface water is restricted to a few large storage dams retaining and damming up these seasonal floods and their runoff. Thus, where people don’t live near perennial rivers or make use of the storage dams, they are dependent on groundwater. The advantage of using groundwater sources is that even isolated communities and those economic activities located far from good surface water sources such as mining, agriculture, and tourism can be supplied from groundwater over nearly 80% of the country.
Document 10: Nigeria: According to the International Organization for Migration, Nigeria witnessed a dramatic increase in remittances sent home from overseas Nigerians, going from USD 2.3 billion in 2004 to 17.9 billion in 2007. The United States accounts for the largest portion of official remittances, followed by the United Kingdom, Italy, Canada, Spain and France. On the African continent, Egypt, Equatorial Guinea, Chad, Libya and South Africa are important source countries of remittance flows to Nigeria, while China is the biggest remittance-sending country in Asia.
Document 11: Sahara: To the north, the Sahara skirts the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Maghreb, the Sahara borders the Mediterranean forest, woodland, and scrub ecoregions of northern Africa, all of which have a Mediterranean climate characterized by hot summers and cool and rainy winters. According to the botanical criteria of Frank White and geographer Robert Capot-Rey, the northern limit of the Sahara corresponds to the northern limit of date palm cultivation and the southern limit of the range of esparto, a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the 100 mm (3.9 in) isohyet of annual precipitation.
Document 12: Geography of Nigeria: Nigeria, like the rest of West Africa and other tropical lands, has only two seasons. These are the dry season and the rainy season. The dry season is accompanied by a dust laden airmass from the Sahara Desert, locally known as Harmattan, or by its main name, The Tropical Continental (CT) airmass, while the rainy season is heavily influenced by an airmass originating from the south atlantic ocean, locally known as the south west wind, or by its main name, The Tropical Maritime (MT) airmass. These two major wind systems in Nigeria are known as the trade winds.
Document 13: Nigeria: Nigeria is often referred to as the ``Giant of Africa '', owing to its large population and economy. With 186 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has the third - largest youth population in the world, after India and China, with more than 90 million of its population under age 18. The country is viewed as a multinational state as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages and are identified with a wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims, who live mostly in the north. A minority of the population practise religions indigenous to Nigeria, such as those native to the Igbo and Yoruba ethnicities.
Document 14: List of African countries by GDP (PPP): Region Rank Country 2015 GDP (PPP) millions of International dollars -- Africa 5,736,700 Nigeria 1,192.00 Egypt 995.97 South Africa 724.01 Algeria 570.64 Morocco 274.53 6 Angola 185.25 7 Sudan 167.42 8 Ethiopia 159.22 9 Tanzania 150.4 10 Kenya 143.05 11 Tunisia 127.21 12 Ghana 113.35 13 Libya 92.88 14 Uganda 79.75 15 Ivory Coast 78.34 16 Cameroon 72.11 17 Zambia 64.65 18 Democratic Republic of the Congo 63.27 19 Botswana 37.16 20 Senegal 36.30 21 Madagascar 35.56 22 Gabon 34.41 23 Chad 33.73 24 Mozambique 32.00 25 Burkina Faso 31.18 26 Mali 29.15 27 Zimbabwe 28.90 28 Republic of the Congo 27.92 29 Equatorial Guinea 25.94 30 Mauritius 24.84 31 Namibia 24.51 32 Benin 21.16 33 Malawi 20.56 34 Rwanda 20.32 35 Niger 18.96 36 Mauritania 16.43 37 Guinea 15.28 38 Swaziland 10.87 39 Togo 10.82 40 Eritrea 7.94 41 Burundi 7.88 42 Somalia 5.90 43 Lesotho 5.78 44 Gambia 3.27 45 Liberia 3.78 46 Cape Verde 3.48 47 Djibouti 3.09 48 Seychelles 2.53 49 Guinea - Bissau 1.94 50 Central African Republic 1.62 51 Comoros 1.21 52 São Tomé and Príncipe 0.66
Document 15: Geography of Nigeria: With the Intertropical Convergence Zone (ITCZ) swinging northward over West Africa from the Southern Hemisphere in April, heavy showers coming from pre-monsoonal convective clouds mainly in the form of squall lines also known as the north easterlies formed mainly as a result of the interactions of the two dominant airmasses in Nigeria known as the Maritime tropical (south westerlies) and the Continental tropical (north easterlies), begins in central Nigeria while the Monsoons from the south atlantic ocean arrives in central Nigeria in July bringing with it high humidity, heavy cloud cover and heavy rainfall which can be daily occurrence lasting till September when the monsoons gradually begin retreating southward to the southern part of Nigeria. Rainfall totals in central Nigeria varies from 1,100 mm (43.3 in) in the lowlands of the river Niger Benue trough to over 2,000 mm (78.7 in) along the south western escarpment of the Jos Plateau.
ground_truth: savannah
sub_queries: What is the largest economy in Africa? Answer: Nigeria
What type of vegetation is in central Nigeria ? Answer: savannah