Universities and colleges 1,008 Urbanization 453 Urban policy 259 Urban renewal 255 Unemployment 185 Ultrasonic imaging 180 Urban ecology (Sociology) 172 Utopias 150 User interfaces (Computer systems) 111 Urban poor 107 Usage 99 Ultrasonography 91 Underground movements 87 Urban economics 79 Uncertainty 75 User-Computer Interface 67 Universities 63 Upper class 61 Underwater archaeology 57 Urban transportation 56 Utilization 56 Urban ecology (Biology) 55 United States 51 Utopias in literature 51 Unconscious, Psychology 47 Urban schools 47 Unemployed 46 Urban health 46 Underground Railroad 45 Urban youth 43 Ukrainians 38 User-generated content 36 Utilitarianism 36 Ubiquitous computing 33 Urban Health 33 Urban anthropology 31 Urinary organs 30 Urban agriculture 29 User-centered system design 27 Urban geography 26 Undercover operations 25 Underground press publications 25 Unmarried couples 25 Urban Renewal 24 Underachievers 23 Underground areas 22 Uncertainty (Information theory) 21 Undocumented Immigrants 21 Undocumented immigrants 21 United States Government Agencies 21 Uranium mines and mining 21 Urban violence 21 Urologic Diseases 21 Underwater exploration 20 Urban Indians 20 Urban landscape architecture 20 Urology 20 Unidentified flying objects 19 Urdu language 19 Underground construction 18 Undertakers and undertaking 18 Unjust enrichment 18 Unmarried mothers 18 Urinary catheterization 18 U.S. states 17 Ultrasonography, Prenatal 17 Unemployment insurance 17 Urban warfare 17 Unity 16 University cooperation 16 Urban-rural migration 16 Urinary incontinence 16 Utopian socialism 16 Underground literature 15 Universals (Philosophy) 15 UnrealScript (Computer program language) 15 Urban women 15 Ut pictura poesis (Aesthetics) 15 Unaccompanied immigrant children 14 Unified operations (Military science) 14 Universalism 14 Unskilled labor 14 Upper class women 14 Urban runoff 14 Use 14 Ubuntu (Philosophy) 13 Ultrasonic waves 13 Ultrasonics in obstetrics 13 Urban transportation policy 13 Uterine Cervical Neoplasms 13 Uighur (Turkic people) 12 Ultra-Orthodox Jews 12 Uncles 12 Unemployed youth 12 Uranium 12 Urban dialects 12 Urban parks 12 Ulama 11 Unified field theories 11 Unitarian Universalist churches 11