predominantly rural, with a few large towns; dwellings are evenly spread throughout the country. The only sparsely populated area of the country is the savanna land in the former province of Umutara and Akagera National Park in the east. Kigali is the largest city, with a population of around one million. Its rapidly increasing population challenges its infrastructural development. According to the 2012 census, the second largest city is Gisenyi, which lies adjacent to Lake Kivu and the Congolese city of Goma, and has a population of 126,000. Other major towns include Ruhengeri, Butare, and Muhanga, all with populations below 100,000. The urban population rose from 6% of the population in 1990, to 16.6% in 2006; by 2011, however, the proportion had dropped slightly, to 14.8%. Rwanda has been a unified state since pre-colonial times, and the population is drawn from just one cultural and linguistic group, the Banyarwanda; this contrasts with most modern African states, whose borders were drawn by colonial powers and did not correspond to ethnic boundaries or pre-colonial kingdoms. Within the Banyarwanda people, there are three separate groups, the Hutu, Tutsi and Twa. The CIA World Factbook gives estimates that the Hutu made up 84% of the population in 2009, the Tutsi 15% and Twa 1%. The Twa are a pygmy people who descend from Rwanda's earliest inhabitants, but scholars do not agree on the origins of and differences between the Hutu and Tutsi. Anthropologist Jean Hiernaux contends that the Tutsi are a separate race, with a tendency towards "long and narrow heads, faces and noses"; others, such as Villia Jefremovas, believe there is no discernible physical difference and the categories were not historically rigid. In precolonial Rwanda the Tutsi were the ruling class, from whom the kings and the majority of chiefs were derived, while the Hutu were agriculturalists. The current government discourages the Hutu/Tutsi/Twa distinction, and has removed such classification from identity cards. The 2002 census was the first since 1933 which did not categorise Rwandan population into the three groups. Education Prior to 2012, the Rwandan government provided free education in state-run schools for nine years: six years in primary and three years following a common secondary programme. In 2012, this started to be expanded to 12 years. A 2015 study suggests that while enrollment rates in primary schools are "near ubiquity", rates of completion are low and repetition rates high. While schooling