Roads 326 Harbors 166 History 82 Maps 20 World maps 15 Historical geography 9 Discovery and exploration 6 more ... Indians of North America 6 Civilization 5 Election 5 Presidents 5 World politics 5 Emigration and immigration 4 Foreign relations 4 Population 4 World War, 1914-1918 4 World War, 1939-1945 4 World history 4 Atlases 3 Migrations 3 Politics and government 3 Slave trade 3 Social conditions 3 Trade routes 3 Agriculture 2 Antiquities 2 Census districts 2 Cold War 2 College facilities 2 Description and travel 2 less ...