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hypsometry : The study or measurement of land elevation relative to mean sea level. Hypsometry is the terrestrial equivalent of bathymetry.

hypsography : The geographic representation on a map of features related to elevation, altitude, and other measures of height above a reference surface.

hydrosphere : The totality of the water found on, under, and above the Earth’s surface in liquid, solid, and gaseous forms, including all oceans, lakes, rivers, and streams, as well as all ice and glaciers and subsurface groundwater. Some definitions restrict the hydrosphere to liquid water only, instead placing solid forms in the cryosphere and gaseous forms in the atmosphere.

hydrography : The study of the surface waters of the Earth

humus : Partially decomposed organic soil material.

hummock : A small knoll or mound, typically less than 15 metres (49 ft) in height and situated above an otherwise level ground surface.

human geography : The branch of geography that studies humans and their communities, cultures, economies, and interactions with the environment by examining their relations with and across space and place. Along with physical geography, it is one of the two major sub-fields of geography.

hotspot : An area in the middle of a lithospheric plate where magma rises from the mantle and erupts at the Earth’s surface. Volcanoes sometimes occur above a hotspot.

horst : A raised block of the Earth’s crust, bounded by parallel escarpments or faults, that has been displaced upward or has remained stationary while adjacent blocks on either side, known as grabens, have been displaced downward. Horsts and grabens often occur side-by-side in a repeated series of vertical displacements.

horn : A mountain formed by the back-to-back abutment of three or four adjacent cirques, leaving a distinctly pyramidal peak.

horizon: Also called the skyline.

The apparent line that separates the ground from the sky, dividing all visible directions into two categories: those that intersect the Earth’s surface and those that do not. When not obscured by buildings, trees, or mountains, the true horizon can be useful in navigation and determining positional orientation.

hogback : Also hog’s back.

A long, narrow ridge or series of hills with a narrow crest and steep, symmetrical slopes of nearly equal inclination on both flanks, especially one created by the erosion of an outcropping which exposes homoclinal sedimentary rock strata.

historical geography : A branch of human geography that studies the ways in which geographic phenomena have changed over time, especially (though not necessarily limited to) geographic change as it relates to human activity.

hinterland : An area that is tributary to a place and linked to that place through lines of exchange or interaction.

hillock : Also called a knoll.

A small hill.

hill : Any landform that extends above the surrounding terrain. A hill is generally considered less steep than a mountain.

highway : Any major public or private road or other thoroughfare on land, especially one that is paved and capable of supporting high-capacity, rapid transit between populated places.

highland: Sometimes used interchangeably with upland.

1.  Any elevated region of land, often one that is mountainous or situated atop a plateau. The term is sometimes reserved for relatively low-elevation mountain ranges or foothills.2.  Any area of land (mountainous or otherwise) that is higher in elevation relative to another area. In this sense, the term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level.

hemisphere : Half of the Earth, usually conceived as resulting from the division of the globe into two equal parts of either north and south or east and west

hedgerow: Also simply called a hedge.

A line of closely spaced shrubs or trees, planted and trained so as to form a barrier, to mark the boundary between two neighboring areas, or to serve as a windbreak for crops in adjacent fields.

heath: Also called heathland.

A shrubland habitat found mainly on free-draining, infertile, acidic soils and characterized by open, low-growing, woody vegetation.

heartland : 1.  The central part of a region.2.  A part of a region considered essential to the viability and survival of the whole.

hearth : The source area of any innovation. The source area from which an idea, crop, artifact, or good is diffused to other areas.

headwall : A steep slope or sheer cliff face at the upper end of a valley (e.g. at the back of a cirque), or at the active face of a mine, pit, or quarry

headland : A high coastal promontory that extends out into a body of water, often surrounded by steep cliffs. A very large headland is often called a cape.

heading : The compass direction in which the bow or nose of a moving vessel or aircraft is pointed. This is not necessarily the same direction in which the vessel is actually traveling, known as its course; any difference between heading and course is due to the motion of the air or water through which the vessel is moving, or other aerodynamic effects such as skidding or slipping. See also bearing.

harmonic tremor : One of a series of continuous rhythmic earthquakes in the Earth’s upper lithosphere that can be detected by seismographs. Harmonic tremors often precede or accompany volcanic eruptions.

hanging valley : A tributary valley that is higher in elevation than the main valley into which it drains, such that it appears to be “hanging” above the lower valley. Hanging valleys are commonly the result of differential glacial erosion, when adjacent areas beneath a glacier are subjected to different rates of erosion.

hamlet : A small human settlement, variably defined as one the size of a town, village, or parish or as a smaller subdivision of or satellite entity to a larger settlement.

hachure : Any of a series of non-numerical lines used on a map to indicate the general orientation and steepness of topographical terrain. Such lines vary in length, thickness, and spacing, with steeper slopes indicated by shorter, heavier, and more closely spaced lines

guyot: Also tablemount.

An isolated underwater seamount with a flat top that is at least 200 metres (660 ft) below the water’s surface.

gully : A landform resembling a large ditch or a small ravine created by the action of swift running water eroding deeply and sharply into soil, typically on a hillside.

gulf : A large arm or inlet of an ocean or sea that lies within a curved coastline, similar to a bay but usually larger and often with a narrower opening.

gulch: A deep, V-shaped valley formed by erosion, often containing a small stream or a dry streambed, especially one in arid regions.

groyne : A rigid, man-made hydraulic structure extending from an ocean shore or river bank, constructed to interrupt water flow and limit the movement of sediment by longshore drift.

growing season : The part of the year during which local weather conditions (i.e. temperature and precipitation) permit the normal growth of plants in a given location. What defines a “growing season” is often informal and colloquial, and may vary widely by location and from year to year; in many places, the local growing season is defined as the period of time between the average date of the last frost (in temperate parts of the Northern Hemisphere, this typically occurs in the spring) to the average date of the first frost (in the autumn).

grove : A small group of trees growing close together and generally surrounded by little or no undergrowth.

groundwater : The water present beneath the Earth’s surface in soil pore spaces and in fractures and voids within geological strata. Contrast surface water.

grid north : The direction northwards as indicated by the grid lines of a map projection, which may or may not be aligned with geodetic north. Grid north may also differ from magnetic north.

grid : A pattern of lines on a chart or map, such as those representing latitude and longitude, which helps determine absolute location.

great-circle distance: Also orthodromic distance.

A route which follows the arc of a great circle as defined by the intersection of the Earth’s surface with an imaginary plane passing through the Earth’s center. It is the shortest route between two places on the Earth’s surface.^[

great circle: Also orthodrome.

Any circle on the surface of a sphere created by the intersection of the sphere and a plane that passes through its center. A great circle divides the sphere into two equal hemispheres, and all of a sphere’s great circles have the same center and circumference as each other, which by definition is the largest possible circumference of the sphere. The mathematical properties of great circles make them useful in geodesy, where they are often visualized upon the surface of the Earth (despite the fact that the Earth is not a perfect sphere): for example, the Equator of the idealized Earth is a great circle, and any meridian with its antimeridian forms a great circle. Because the shortest path between any two points on the surface of a sphere follows the arc of a great circle, great-circle distances are often used as approximations of geodesics for the purposes of air and sea navigation.

graticule : A network of lines on a map or chart (or imagined on the surface of the Earth) representing geodetic parallels of latitude and meridians of longitude

graben : A depression or valley bounded on either side by distinct, parallel escarpments or faults and formed by the downward displacement of a block of the Earth’s crust. Grabens often occur side-by-side with horsts, their uplifted or non-displaced counterparts, in a repeated series of vertical displacements.

gnamma See panhole.

globalization : The process of interaction and integration among people, companies, governments, and cultures across the world. A complex and multifaceted phenomenon, globalization is considered largely the result of economically motivated advances in transportation and communication technologies in the past several centuries which have dramatically increased interactions between otherwise isolated groups of people.

Global Positioning System (GPS) : A satellite-based radionavigation positioning system owned and operated by the United States Department of Defense and made available for use by both the military and the general public. It is one of several GNSS standards that provides geolocation and time information, transmitted via microwave signals, to enabled satellite navigation devices, known as GPS receivers, anywhere on or near the Earth where there is an unobstructed line of sight to at least four GPS satellites. Modern state-of-the-art GPS receivers can accurately pinpoint locations to within 30 centimetres (0.98 ft).

global city : Also world city, power city, or alpha city.

A city which functions as an important or primary node in the global economy. Though criteria are not strictly defined, a global city typically is very large; dominates trade and economic interactions within a large surrounding area; supports a large and demographically diverse population; serves as a center of ideas and innovation in business, science, culture, and politics; and/or is a headquarters for major financial institutions, multinational corporations, or worldwide media and communications networks.

glen : A long valley bounded by gently sloping, concave sides, and typically narrower and deeper than a strath. The term is used primarily in Scotland.

glade: Also clearing.

Any large, open, mostly treeless area within a forest.

glacier : A persistent mass of dense ice that is constantly moving under its own weight, and which is composed largely of compacted snow that forms where the annual accumulation of snow exceeds its melting and sublimation over very long periods of time. Glaciers slowly deform and abrade the land beneath them, creating a huge variety of landforms including cirques, moraines, and fjords. They form exclusively on land and are distinct from the much thinner ice that forms on bodies of water.

glaciation : 1.  The process or state of being covered with a glacier.

2.  Another name for a glacial period, an interval of time that is marked by colder temperatures and advancing glaciers.

glacial till: The mass of rocks and finely ground material carried by a glacier and deposited when the ice melts. This creates an unstratified material of varying composition.

ghetto : A section of a city occupied by members of a minority group who live there because of social restrictions on their residential choices. Originally, the term referred specifically to a section of a European city to which Jews were confined

geostatistics : A branch of statistics which involves the organization, management, and analysis of spatial and spatiotemporal datasets. Geostatistical algorithms are often incorporated in GIS software applications.

geosphere : The collective non-living parts of the Earth: the lithosphere, the atmosphere, the cryosphere, and the hydrosphere

geoscience : See Earth science.

geomorphology : The study of the arrangement and form of the Earth’s crust and of the relationship between these physical features and the geologic structures beneath