| absolute location | a point on the earth's surface expressed by a coordinate system such as latitude and longitude |
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| accessibility | the ability to reach a place with respect to another place |
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| acculturation | modification in a culture by the adoptation of outside cultural traits |
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| aeolian | relating to wind action - erosion or transportation by wind; also eolian. named after the greek god of the winds - aeolus |
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| aerial photograph | a photograph of a portion of the earth's surface, often from airplane |
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| age-sex pyramid | a bar graph which displays the age and sex distribution of a population. population pyramid |
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| albedo | the proportion of radiation reflected from a surface |
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| alluvial fan | a broad, circular fan-shaped deposit of sediments found in deserts where erosional stream channels meet the valley floor and spread out, depositing the stream load |
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| alluvium | river deposits, such as silt, sand, and mud |
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| angle of repose | the stable angle that a pile of rocks or a slope wishes to remain at. road cuts are usually much steeper than the angle of repose so debris continues to fall from them until they attain the angle of repose |
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| antipode | the point on the earth's surface exactly opposite of a given point |
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| aphelion | the point when the earth is farthest from the sun during its annual orbit. occurs about july 3 when the earth is 94,555,000 miles away from the sun |
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| aquifer | an underground reservior of water which can be extracted for surface use |
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| atmosphere | the body of air and gas which surrounds the earth |
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| archipelago | a chain or set of islands grouped together |
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| atoll | a circular coral reef that encloses a shallow lagoon |
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| aurora australis | also known as the the southern lights; spectacular colored lights that appear in the sky in the far southern hemisphere. |
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| aurora borealis | also known as the the northern lights; spectacular colored lights that appear in the sky in the far northern hemisphere. |
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| avalanche | a generic term for any slide of snow, ice, and debris |
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