Ubac -a north-facing slope.

UN - United Nations

Underemployment - when people have jobs that do not fully occupy them and so they do not earn sufficient wages to properly cover their needs.

Underpopulation - when the population is not sufficient to make full use of all the resources available and so standards of living are not as high as they could be.

Undeveloped -see economically less developed countries.

UNESCO - the United Nations Educational, Scientific and Cultural Organisation

http://portal.unesco.org/en/ev.php-URL_ID=29008&URL_DO=DO_TOPIC&URL_SECTION=201.html

UNHCR - the United Nations High Commissioner for Refugees. An office of the UN which oversees the welfare of refugees, encouraging recipient governments to grant asylum to genuine requests and sometimes providing financial assistance so that they may do so. http://www.unhcr.org/cgi-bin/texis/vtx/home

Uniform slope – a slope, or part of slope, which has no change in angle. On a map the contour lines will be spaced evenly. If they are evenly spaced close together then the slope is uniformly steep. If evenly spaced some distance apart the slope is uniformly gentle.

Upwelling – the upward limb of a convection current. In geography, usually applied to a convection plume in the mantle or the upward movement of water in an ocean current.

Urban - built-up area. Settlements are usually designated as urban once they have grown large enough to support industries which are not rural in nature. However, no common figure can be put on the necessary size as settlements function differently in different areas due to local circumstances.

Urban climate -the climate of an urban area is distinct from the general conditions for the region in which it is located due to the energy released through human activity.

Urban decay -aging inner city areas often experience a loss of industry meaning fewer jobs and triggering a downward spiral of economic and therefore social decline.

Urban Development Corporations -bodies set up in the 1980s to oversee partnerships between government and the private sector whose goal was to regenerate inner city areas in the UK which had suffered urban decay.

Urban fringe -the mixed marginal area lying outside the established urban area where the rural characteristics are increasingly overshadowed by encroaching urban features such as new housing, shopping centres, industrial estates and the like.

Urban heat island -the higher temperature found over and around an urban area created by the release of solar energy from the solid fabric of the buildings, roads etc., coupled with energy released by human activity such as lighting, heating, air-conditioning and/or vehicles and industry.

Urban land-use -the spatial differences and similarities in certain types of land-use in urban areas which allow tracking of the history of their development and thus can be useful for future planning.

Urban regeneration -the improvement of urban areas which have been in decline.

Urban sprawl -the unchecked spread in the land area occupied by an urban area when development is low-rise and it is felt that space efficiency is not an issue.

Urbanization -the increasing percentage of a population living in urban areas due to rural-urban migration and higher levels of natural increase in the urban areas.

U-shaped valley -see glacial valley.

Utility -an industry providing a service such as power and water.