MILITARY GEOGRAPHY
    FOR PROFESSIONALS AND THE PUBLIC

APPENDIX B:

Glossary of geographical terms

absolute humidity: The weight of water vapor present in a given volume of air, usually expressed as grams per cubic meter or grains per cubic foot.

abyss: Ocean depths beyond the continental slope. See also abyssal plain.

abyssal plain: The ocean floor. See also abyss.

acclimatization: Adaptation to a geographic environment significantly different from that to which one is accustomed.

active layer: Soil near the surface that seasonally freezes and thaws in frigid regions. See also permafrost.

aerocentric: A military mindset that emphasizes air power.

aerodynamic drag: Atmospheric force that slows flight, most notably near Earth's surface where air density is greatest. Resistance above about 60 miles (95 kilometers) takes days, weeks, or months to produce significant effects.

aerospace: Earth's atmosphere plus space. See also atmosphere; space.

Agent Orange: A herbicide that U.S. Armed Forces used extensively to defoliate vegetation that could conceal Communist troops in Vietnam.

air line of communication (ALOC): Any aerial route that nations depend on for commercial or military purposes. See also line of communication.

airspace control: Processes designed to prevent fratricide, enhance air defense, and otherwise promote safe, efficient, flexible air operations within and above an area of responsibility. See also airspace control area; area of responsibility.

airspace control area: Bounded territory within and above an area of responsibility, subdivided as required to ensure safe, efficient, flexible air operations. See also airspace control; area of responsibility.

alluvium: Clay, silt, sand, gravel, and other detritus that rivers deposit downstream.

altitude: Height above mean sea level, mainly applied to positions in the atmosphere above Earth's surface. See also elevation.

amphibious forces: A naval force and a landing force that are organized, equipped, and trained to conduct operations from sea to a hostile or potentially hostile shore.

aquifer: A water-bearing stratum of permeable rock, sand, or gravel.

archipelago: A string of islands, such as the Aleutians and Indonesia.

arctic sea smoke: Maritime fog that occurs most often over the Arctic or Antarctic Oceans when very cold air passes over much warmer water. Occasionally occurs over inland seas when very cold winter air shifts somewhat equatorward. See also fog.

area analysis: A process that assesses geographic influences on military plans, programs, and operations to ascertain probable effects on friendly and enemy courses of action.

area of influence: Territory within which a regional commander could, using weapon systems and mobility means under his or her control, conduct military operations. Such territory may be much larger than the commander's area of responsibility. See also area of responsibility.

area of interest: Territory outside of (but not necessarily contiguous to) a regional commander's area of responsibility that warrants close attention because activities therein could significantly affect military plans, programs, and operations within the commander's AOR. See also area of responsibility.

area of operations: Territory within which military activities of any kind occur. It may include all or a small part of a commander's area of responsibility. See also area of responsibility.

area of responsibility (AOR): Territory within which a regional commander exercises responsibility and authority over, and is accountable for, all military activities by armed forces under his or her control. See also tactical areas of responsibility; theater areas of responsibility.

area orientation: Missions, organizations, equipment, and training that prepare individuals and military formations for projected deployment to a specific geographical region. Repeated, lengthy tours of duty in relevant countries not only help foreign area officers hone their language and cross-cultural skills, but enable them to develop close personal relationships .

aridity: See desert; semi-arid.

arroyo: Spanish for the bed of a narrow, steep-sided stream that dries up seasonally or during droughts (a term most often used in Southwestern United States and Mexico). Heavy rains commonly cause flash floods in such watercourses. See also intermittent stream; wadi.

artesian spring, well: A natural or artificial source of water that hydrostatic pressures force from depths to the surface like a fountain. See also spring.

astrocentric: A military mindset that emphasizes space power.

atmosphere: the envelope of air that surrounds Earth. Air becomes thinner with altitude until the vacuum of space replaces it completely.

atmospheric pressure: The weight that a vertical column of air exerts on any given point below in response to gravitational attraction. Readings are highest at sea level and gradually decrease at greater elevations.

atoll: a circular reef of coral and other materials that encloses a lagoon. See also lagoon.

aurora borealis: "Northern lights;" ghostly displays of colored streamers, rays, arcs, bands, curtains, draperies, sheets, and/or patches that shimmer and flit across skies at high latitudes in the Northern Hemisphere. Called aurora australis in the Southern Hemisphere.

auroral zones: Arctic and Antarctic regions where charged particles ejected from the sun and deflected by Earth's magnetic field disrupt radio frequency propagation.

axis of advance: A control measure, usually a road, identifiable natural terrain corridor, or series of points that commanders order subordinate ground forces to follow from present positions to objectives in enemy territory.

bank: A mass of clouds or fog; a mound or ridge; plains below the ocean surface but above the continental shelf; the sloping margin of an inland watercourse or lake. River banks are designated left or right from viewpoints that face downstream.

bar: A submerged or partly submerged accumulation of alluvium along seashores, rivers, and smaller streams. Such obstructions inhibit or prevent navigation by ships and craft.

baseline: A line, usually the low water line, used to measure the breadth of a coastal state's territorial sea. See also exclusive economic zone; territorial sea.

beach: Relatively horizontal terrain that extends from a coastline inland to the first marked change in topography or vegetative cover. Cliffs and other vertical terrain that rise abruptly from the sea lack beaches.

beachhead: An area on a hostile or potentially hostile coast that, when seized and held, facilitates the continuous landing of troops and materiel. It also affords a base from which to expand operations inland. See also bridgehead.

beginning of morning nautical twilight (BMNT): A period of incomplete darkness before sunrise when the sun is 12 degrees below the celestial horizon.

blackout: The disruption of radio and radar transmissions for minutes or many hours after a nuclear detonation in space ionizes Earth's atmosphere over a wide area. Short-wave, high-frequency propagations are most susceptible. See also electromagnetic pulse.

blizzard: An intensely cold wind of 30 knots or greater velocity that blows snow and thereby reduces visibility to half a mile or less (about one kilometer) at ground level.

"blue water": Naval slang for high seas (open oceans) beyond the littoral.

bog: Spongy, poorly-drained soil variously covered with peat, sedges, heath, mosses, lichens, and other stunted plants. See also marsh; swamp.

boundary: A borderline, sharply- or ill-defined, between countries or military formations. See also frontier.

breakbulk ship: An oceangoing transport that carries undifferentiated dry cargo of various sizes and shapes. See also container ship.

breakwater: A wall or other offshore structure installed to protect a harbor or beach from waves that might damage ships or infrastructure.

bridgehead: An area on the far side of a river in hostile or potentially hostile territory that, when seized and held, facilitates the continuous crossing of troops and materiel. It also affords a base from which to continue offensive military operations or shield key terrain to the rear. See also beachhead.

"brown water": Naval slang for seas along the littoral; the milieu of riverine and swamp operations.

buffer zone: a territorial strip designed to separate the possessor from present or potential external aggressors and thus provide some degree of protection.

calving: The breaking away of ice masses from ice walls, ice shelves, and icebergs.

canal: a manmade channel that connects two or more bodies of water, such as rivers, seas, and oceans; some canals connect inland ports with open water.

canopy: The uppermost layer of foliage within a forest; two or more distinctive tiers typify most tropical rain forests. See also jungle; rain forest.

catch basin or catchment: See drainage basin.

ceiling: See cloud ceiling.

celestial sphere: An imaginary, nonrotating orb of indefinite radius with its center at Earth's core. Its equator is a projection of Earth's equator. Various features afford a frame of reference for locating orbital objects in space. See also declination; right ascension.

change operational control (CHOP): The date, Coordinated Universal Time, and sometimes the place that a military force passes from one commander's jurisdiction to another's. Commonly employed by naval forces.

channel: The deepest and usually swiftest part of any stream; the deepest, most navigable part of any strait; the deepest, most navigable water in harbors.

choke point: A constricted spot along any land or sea route. Such spots are especially vulnerable to interdiction.

circadian rhythm: The 24-hour biological cycle that governs most human activities on Earth. Disruptions due to "jet lag," which lengthy space flights magnify immensely, to greater or lesser degrees cause psychophysical problems such as fatigue, inattentiveness, and emotional instability.

circumterrestrial space: A region that abuts Earth's atmosphere at an altitude of about 60 miles (95 kilometers) and extends to about 50,000 miles (80,000+ kilometers). Most military space missions currently are confined therein.

cislunar space: Wedge-shaped territory between Earth and its moon. One point touches Earth's atmosphere, others touch lunar libration points L-4 and L-5. See also lunar libration points.

clan: A relatively small, tightly knit group of families whose members claim common ancestry or identify with a common totem. See also ethnic group; race; tribe.

climate: Weather patterns discernible from meteorological records that are most reliable when compiled hourly at specified locations over a period of years. Resultant statistics, which reveal means and extremes, indicate probabilities that particular conditions will prevail at particular times on particular days or months at each place. See also meteorology; weather.

cloud: A visible aggregate of minute water or ice crystals suspended in the atmosphere. Air-to-ground visibility by human eyes and most technological sensors is severely limited or nonexistent, whereas surface-to-surface visibility is unaffected. See also fog.

cloud ceiling: The distance between a cloud base and terrain directly below.

cloud cover: The amount of cloud at any given location, stated in eighths (1/8 to 4/8 is scattered; 5/8 to 7/8 is broken; 8/8 is overcast). Several layers of scattered clouds may cause broken or overcast conditions.

COCOA: Acronym for Critical terrain; Obstacles; Cover and concealment; Observation and fields of fire; Avenues of approach. See also OCOKA.

concealment: Protection against nothing more than enemy observation. See also cover.

container ship: An oceangoing transport that carries cargo in rectangular steel boxes that stack vertically in ready-made cells and horizontally on top of strong hatch covers so loading and unloading is rapid and wasted space is negligible. See also breakbulk ship.

continental shelf: A generally undulating submarine plain that declines gently seaward from major land masses. Widths vary from nonexistent to 800 miles or more (1,300 kilometers). Depths usually are less than 100 fathoms (600 feet, 180 meters) See also continental slope.

continental slope: A precipitous incline, generally 10-20 miles wide, that plunges from the continental shelf to the bottom of the oceanic abyss, which is several miles deep in some places. See also abyss; continental shelf.

corduroy: Logs laid at right angles across soggy roads, tracks, and trails to improve vehicular trafficability.

core area: A nationally important, even vital, center or region. See also key terrain.

corps tactical zone (CTZ): The area of responsibility for a corps-size military force.

cover: Protection against the effects of enemy weapons as well as observation. See also concealment.

crest: The top of a mountain, hill, or ridge. See also military crest; topographical crest.

critical terrain: See key terrain.

cultural geography: An interdisciplinary field that deals with spatial variations in learned human behavior, including the geographic diversity of settlements, languages, religions, social structures, the arts, economies, technologies, and other activities. See also geography; military geography; physical geography; political-military geography.

current: The flow of water in any stream, canal, sea, or ocean calculated in terms of direction and velocity.

D-Day: The date that any specified military operation is scheduled to commence or actually commences.

declination: The celestial equivalent of latitude. Specifically, the angular distance north or south of the celestial equator, measured along a great circle that passes through the celestial poles. See also celestial sphere; right ascension.

deep space: Interplanetary space beyond the Earth-Moon System. See also circumterrestrial space; outer space.

defilade: A position protected against enemy flat trajectory weapons; a natural or artificial mask, such as a ridge, hummock, building, or forest, between such weapons and their targets.

defile: A natural or artificial constriction along a surface route, such as a mountain pass, a gorge, a strait, or a narrow city street.

delta: Triangular alluvial deposits at the mouth of a river. Some deltas are small, others such as those of the Nile, Mekong, and Mississippi Rivers measure much more than 100 miles (160 kilometers) on each side. See also alluvium.

demography: The study of human populations, especially size, density, distribution, and other vital statistics. It is an interdisciplinary field that melds geography with mathematics, biology, medicine, sociology, economics, history, and anthropology.

density altitude: Air pressure at mean sea level (29.92 inches of mercury) and 59⁰ F (15⁰ C) corrected to account for greater heights and higher temperatures, which decrease air density and increase density altitude. Density altitude calculations are critically important, because lighter air reduces aircraft motive power, limits lift capacities, demands faster true airspeed and a longer roll for takeoffs, slows rates of climb, requires faster true airspeeds to sustain flight, lengthens rolls after landings, and makes stopping more difficult.

deposition region: A dense radioactive layer that accumulates 25-30 miles (40-48 kilometers) above Earth when a cascade of gamma rays from a nuclear explosion at greater altitude collides with the upper atmosphere. Resultant charge imbalances create electromagnetic pulse. See also electromagnetic pulse.

desert: A region in which average annual precipitation generally measures less than 10 inches (25 centimeters). Arctic regions that receive a bit less fail to qualify, because evaporation is slow. Hot regions that receive a bit more qualify, because evaporation is rapid. Deserts may be mountainous or flat, sandy or stony. See also semiarid.

dewpoint: The temperature at which water vapor turns into water droplets through a process called condensation.

Distant Early Warning (DEW) Line: A string of radar stations across the arctic from the Aleutian Islands to the Atlantic Ocean, installed during the Cold War to alert U.S. and Canadian defenders of a surprise Soviet attack over the North Pole.

diurnal: A daily occurrence or cycle.

divide: A watershed between two drainage basins. See also drainage basin.

doldrums: An atmospheric belt astride the equator, characterized by calms that shifting breezes and squalls intermittently interrupt.

drainage basin: Lands on one side of a topographical divide that accumulate rainfall and snow, then distribute runoff to lower elevations via a system of small streams that are tributary to rivers.

drift: Ocean current velocity. See also current; set.

drop zone (DZ): An area into which transport aircraft deliver troops, equipment, and supplies by parachute.

Earth-Moon System: Space and all its contents within an imaginary sphere that extends approximately 480,000 miles (772,000 kilometers) in every direction from Earth's core. Large, solid matter is confined mainly to Earth, its moon, and asteroids, but invisible atmosphere, gravity, and the Van Allen radiation belts are immensely important.

electromagnetic pulse (EMP): Prodigious current that results from a nuclear explosion in the upper atmosphere or space, peaks 100 times faster than lightning, then bolts toward Earth. Unshielded electronics within several hundred miles of the epicenter may be disabled. See also deposition region.

elevation: Height above mean sea level. Applied mainly to positions on Earth's surface. See also altitude.

enclave: Foreign territory within a country or coalition. East Germany, for example, enclosed West Berlin throughout the Cold War. See also exclave.

end of evening nautical twilight (EENT): Occurs after sundown when the sun is between the horizon and 12 ⁰F below.

environment: Geographical circumstances that prevail at any given place; the sum total of all biological, chemical, and physical factors to which organisms are exposed.

estuary: An arm of the sea into which fresh water streams empty and mingle with intruding salt water tides.

ethnic group: Culturally distinctive peoples with common physical characteristics, customs, language, religion, and traits. See also clan; race; tribe.

exclave: Part of a country or coalition enclosed within the territory of a foreign power. West Berlin, for example, lay entirely inside East Germany throughout the Cold War. See also enclave.

exclusive economic zone (EEZ): A maritime area adjacent to territorial seas that is subject to legal provisions embedded in the United Nations Convention on Law of the Sea. Coastal states are authorized to exercise sovereignty over natural resources and jurisdiction over some scientific research and environmental projects within the EEZ. The outer limit may coincide with the outer edge of the continental shelf in some cases. See also continental shelf; territorial sea.

exosphere: Earth's atmosphere from an altitude of about 300 miles (480 kilometers) to 2,000+ miles (3,200+ kilometers), where it terminates in a hard vacuum.

exterior lines of communication: Relatively long routes that lead to any given area of operation from distant positions. Such routes not only make it difficult for military commanders to concentrate armed forces rapidly at decisive points and sustain them after arrival but may also be difficult to safeguard if they traverse hostile territory. See also interior lines of communication; line of communication.

fallout: See radioactive fallout.

fast ice: Sea ice that forms along, and remains attached to, coasts. It extends in some places as far out as the 10-fathom curve (60 feet, 18 meters) in late winter. See also ice shelf.

fetch: The distance over open seas that winds blow without a significant change in direction. Wind speeds and fetch determine wave heights.

field fortification: See fortification.

fire support coordination line (FSCL): An imaginary line, preferably drawn along well-defined terrain features, used to control fire support of military operations. It is drawn to ensure maximum freedom of military action, yet to minimize "fratricide" and aerial interference with ground schemes of maneuver.

fog: A cloud in contact with or just above ground level. Thin fog limits surface-to-surface visibility to no more than 1 nautical mile (1.3 kilometers); visibility in dense fog is 50 yards (45 meters) or less. See also arctic sea smoke; cloud: sea smoke.

folkways: Customary modes of thinking, feeling, and acting common to a social group. Key considerations include traditions, values, motivations, hopes, fears, and taboos; manners and mannerisms; religious beliefs; rites, rituals, and holidays; behavior patterns; social hierarchies; lines of authority; moral codes; sexual mores; work ethics; dietary regimes.

footcandle (fc): A unit of illumination equal to one lumen per square foot (929 square centimeters). Full sunlight at zenith produces about 10,000 fc on a horizontal surface; full moonlight provides about 0.02 fc. Illumination for steady reading demands about 10 fc.

fort: Any permanent strongpoint or fortified line occupied exclusively or primarily by a military garrison. The most durable are mainly subterranean. Modern construction materials favor stone, concrete, and steel. See also fortification; fortress.

fortification: Any permanent strongpoint or fortified line; temporary field fortifications typified by foxholes and weapon pits as well as elaborate trench and bunker systems. See also fort; fortress.

fortress: A permanent strongpoint, such as a castle or walled city, designed primarily to protect civilian inhabitants. See also fort; fortification.

frontier: Territory that parallels and somewhat overlaps the boundary between countries. See also boundary.

geography: An interdisciplinary field that studies the Earth, including land, sea, air, space, and all life within those mediums. See also cultural geography; military geography; physical geography; regional geography.

geopolitics: Interactions between geography and foreign policies; governmental policies that emphasize such relationships.

geostationary orbit: The only geosynchronous orbit that circles 22,300 miles (35,887 kilometers) above Earth's equator. Spacecraft on that path appear to stand still when viewed from Earth's surface, because they constantly maintain the same relative position. See also geosynchronous orbit; orbital period.

geosynchronous orbit: Any eliptical flight path that makes figure eights from a center line over Earth's equator at an average ground track altitude of 22,300 miles (35,887 kilometers). Spacecraft on such paths complete precisely one trip per day, because their 24-hour period is the time it takes Earth to rotate once. See also geostationary orbit; orbital period.

glacier: A mass of compacted snow and ice that continually moves from higher to lower ground or, if afloat, spreads continuously. Various types include island ice sheets, ice shelves, ice streams, ice caps, ice piedmonts, cirques, and mountain (valley) glaciers.

Global Positioning System (GPS): A U.S. Department of Defense-operated, spaced-based, radio-navigation system that in 1997 consisted of 24 satellites plus ground support. GPS precisely computes latitude, longitude, altitude, and time for fixed and mobile users wherever they may be. Such information is invaluable for navigational and weapon control purposes.

grade; gradient: A longitudinal slope, the steepness of which can be calculated by dividing the vertical rise or fall by the horizontal distance. A 23-foot rise or fall in 100 feet is a plus or minus 23% grade.

gravity (g): A force of mutual attraction between bodies as a result of their mass. Earth and its moon influence all matter within their respective fields. The effects of both fields diminish with the square of the distance from each source. One g is equivalent to the acceleration of gravity on a body at sea level. See also gravity well.

gravity well: Imaginary, funnel-shaped walls, steep at the bottom but level on top. Greater energy is required to climb out (gravity hinders) than to maneuver on top (where gravity is slight) or drop down (gravity helps). See also gravity.

great circle: Any ring formed by the intersection of Earth's surface with a plane that passes through Earth's center. A great circle is the shortest distance between any two or more points on such an arc.

"green water": Naval slang for solid waves (not sea spray) that wash over ships during storms or heavy weather, where they may damage equipment or wash crew members overboard.

harbor: A sheltered coastal location, natural or improved, that protects ships and smaller craft from winds and waves when they are not at sea. See also seaport.

hardstand: A stabilized soil or paved parking area at an airfield.

hazardous material (HAZMAT): Toxic and infectious wastes that require special treatment, storage, transportation, and disposal.

hazardous waste: Toxic, infectious, flammable, corrosive, explosive, and radioactive substances that await disposal.

H-Hour: The specific time on D-Day that any specified military operation is scheduled to commence or actually commences. See also D-Day.

high earth orbit: A flight path in circumterrestrial space above geosynchronous altitude, between 22,300 and 50,000-60,000 miles from Earth's surface (35,887 to 80,465-96,560 kilometers).

horse latitudes: Two atmospheric belts centered on 30 degrees north and 30 degrees south latitude, characterized by high barometric pressures and calms that shifting breezes occasionally interrupt.

humidity: Water vapor in the air. See also absolute humidity; relative humidity.

hydrology: A science that deals with the physical and chemical properties, transformations, combinations, and movements of water on Earth, including precipitation, its discharge into seas, evaporation, and return to the atmosphere.

hypothermia: A consequence of prolonged exposure to cold or wet conditions that cause human body temperature to drop below normal with deleterious, even fatal, effects.

hypoxia: A condition that occurs when body tissues receive insufficient oxygen, especially at high elevations and altitudes.

iceberg: A large chunk of fresh water ice, floating or aground, that a glacier has calved. See also calving; fast ice; glacier; ice floe.

ice floe: Floating sea water (salty) ice, more common than icebergs, that originates as slush, separates into "pancakes," then forms sheets. Some floes drift out of the Arctic Basin the first year, while those that remain become much harder and thicker. Often called pack ice. See also fast ice; iceberg; ice floe.

ice shelf: See fast ice.

illumination: A measure of sunlight, moonlight, starlight, and luminescent atmosphere. See also footcandle; light data.

infrastructure: All bases, facilities, other permanent or semi-permanent installations, and fabrications used to equip, train, control, move, and otherwise support armed forces.

inland waterway: Any river, stream, canal, lake, or interior sea that serves as a transportation route.

inner space: See circumterrestrial space.

instrument flight rules (IFR): Air traffic control regulations that limit flight clearances to pilots proficient in the use of navigational gear and to aircraft so equipped when low cloud ceilings, poor visibility, or other weather conditions are below specified minimums. See also Visual Flight Rules.

interior lines of communication: Relatively short, secure routes within any given area of operation that provide mobility advantages not available to enemy forces. Such routes enable military commanders to concentrate armed forces most rapidly at decisive points inside or near that area and sustain them after arrival. See also exterior lines of communication; line of communication.

intermittent stream: Any inland watercourse that dries up seasonally or during droughts. Common in deserts. See also arroyo; wadi.

ionosphere: A region of electrically charged (ionized) thin air layers that begins about 30 miles above Earth's atmosphere (48 kilometers) and overlaps the lower exosphere. The maximum concentration of electrons occurs at about 375 miles (600 kilometers). Effects on high frequency radio propagation are important. See also exosphere.

isothermal area: A region within which temperatures remain constant.

jetty: A breakwater that connects with the shore. See also breakwater; mole.

jungle: Tropical or subtropical woodlands with dense primary or secondary undergrowth. See also rain forest.

key terrain: Any geographical point or distinctive area the seizure, retention, destruction, or control of which would confer a marked (preferably decisive) advantage on any military force.

lagoon: A shallow body of normally placid sea water between a reef or other offshore barrier and an island or the mainland. See also atoll.

landing zone (LZ): A prepared or extemporaneous site suitable for operations by helicopters or fixed-wing aircraft with very short or vertical takeoff and landing capabilities.

latitude: The angular distance north and south from Earth's equator measured through 90⁰. See also longitude.

lead: Any long crack or fracture through sea ice that is navigible by ships or smaller craft. Icebreakers look for and enlarge such passageways.

libration points: See lunar libration points.

light data: Tables that for particular periods and places compute morning and evening twilight, sunrise, sunset, moonrise, moonset, and moon phases. See also footcandle; illumination.

line of communication (LOC): Any foreign or domestic land, sea, air, or space route that nations depend upon for commercial purposes; any such route that military commanders use to deploy, employ, sustain, and control armed forces. See also air line of communication; exterior line of communication; interior line of communication; sea line of communication.

line-of-sight: An unobstructed view from point A to point B.

littoral: A coastal region that, for purposes of this document, extends no more than 100 miles (185 kilometers) seaward from the shoreline and an equal distance inland.

local relief: Differences in elevation between high and low ground within any given territory on Earth, its moon, or other planet. See also relief.

longitude: Meridians through any given place expressed in degrees east and west of the Prime Meridian (zero degrees), which passes through the original site of the Royal Observatory in Greenwich, England. See also latitude; meridian.

low earth orbit (LEO): Any flight path in circumterrestrial space between sensible atmosphere and the bottom of the Van Allen belts (60-250 miles, 95-400 kilometers), with some leeway in both directions. Elliptical orbits may dip in and out of LEO during each trip around Earth.

lunar libration points: Five three-dimensional positions in space, all influenced by the gravitational fields that surround Earth and its moon. L1, L2, and L3, on a line with Earth and the moon, are considered unstable. Spacecraft probably would have to expend energy to remain long at those locations. L4 and L5, 60⁰ ahead of and behind the moon in its orbit, are considered stable. Spacecraft probably could remain at those locations indefinitely without expending fuel, because gravitational fields are in balance.

magnetosphere: A vast region dominated by Earth's magnetic field, which traps charged particles, including those in the Van Allen belts. The magnetosphere begins in the upper atmosphere, where it overlaps the ionosphere, and extends several thousand miles farther into space. See also ionosphere.

marecentric: A military mindset that emphasizes sea power.

marginal ice zone (MIZ): A region of more or less mushy ice affected somewhat by waves and swell between open sea water and solid ice closer to shore. Widths vary from a few to about 50 miles (80 kilometers), depending on temperatures, winds, and currents.

marsh: Spongy, wet, or watery meadows covered with tall grass, reeds, and cattails. See also bog; swamp.

megalopolis: An immense urban area populated by at least 10 million people.

meridian: A great circle on Earth's surface that passes through the North and South Poles. See also great circle; longitude.

mesosphere: Atmosphere 30-50 miles (48-80 kilometers) above Earth's surface. Temperature inversions that occur in the stratosphere cease. Thermometer readings of -100 ⁰F (-73 ⁰C) are normal. See also stratosphere.

meteorology: A science that concerns atmospheric phenomena, especially weather conditions and forecasting.

military crest: The highest point on any slope, often lower than the peak, from which views are unobstructed all the way to the bottom. See also crest; topographical crest.

military geography: A geographic specialty that concerns all physical, cultural, and other environmental influences over military policies, plans, programs, and combat/support operations at all levels in global, regional, and local contexts. See also cultural geography; geography; geopolitics; physical geography; political-military geography.

mirage: An optical phenomenon that makes objects seem distorted, displaced (raised or lowered), magnified, multiplied, or inverted due to atmospheric refraction that occurs when a layer of air near Earth's surface differs greatly from surrounding air. Common in desert heat.

mole: A jetty with a road on top. See also breakwater; jetty.

neap tides: Tides about 20% lower than average, which occur twice a month when the sun offsets the moon's gravitational pull at the time of 1st and 3d quarters and the sun and moon are at right angles. See also spring tides; tides.

nuclear fallout: See radioactive fallout.

observation: The ability of military personnel or sensors to see objects within any given area.

obstacle: Any natural or manmade object that prevents, delays, or diverts the movement of military forces.

oceanography: A science that deals with the seas, especially their boundaries, depths, the physics and chemistry of salt water, underwater topography, marine biology, and resources.

OCOKA: Acronym for Observation and fields of fire; Cover and concealment; Obstacles; Key terrain; Avenues of approach. See also COCOA.

open city: Any urban center that enemies on request agree to refrain from or cease attacking, but generally may occupy unopposed.

orbit: The path of any object that flies through space in accord with the physical laws of energy and momentum. Spacecraft that circumnavigate Earth must maintain enough velocity to counterbalance gravity, but not enough to overcome its pull.

orbital period: The time it takes a spacecraft or other object to circumnavigate Earth, its moon, or another planet.

outcrop: Any bedrock exposed on the surface.

outer space: All of the Earth-Moon System except circumterrestrial space. It extends from about 50,000 miles (80,465 kilometers) above Earth's surface to about 480,000 miles (772,000 kilometers), twice the distance from Earth to its moon. See also circumterrestrial space; deep space.

pack ice: Any sea ice, other than fast ice, no matter what form or how disposed. See also fast ice.

permafrost: Perennially frozen soil at various depths beneath Earth's surface in frigid regions. See also active layer.

permeability: The capacity of porous rocks and soils to hold or transmit water.

physical geography: An interdisciplinary field that deals with all Earth and space sciences. Typical topics include astronomy, biology (plant and animal life), climatology, geology, geomorphology (land forms), hydrography, meteorology, oceanography, and pedology (soil sciences). See also cultural geography; military geography; political-military geography.

physiography: See physical geography.

pier: A wharf that projects into harbor waters and thus provides berths on both sides (sometimes at the head as well). See also quay; wharf.

plimsoll lines: Markings drawn on the hull of a cargo ship to indicate whether it is safely loaded.

political-military geography: An interdisciplinary field that concerns relationships between foreign policy, military affairs, and geography. Typical topics include areas of responsibility, diplomacy, foreign relations, dissimilar military Service perspectives, strategy, operational art, and tactics. See also cultural geography, geography; military geography; physical geography.

port: See seaport.

precipitation: Moisture that falls from clouds. Air and surface temperatures determine whether precipitation takes the form of rain, snow, sleet, hail, or icy glaze.

pressure: See atmospheric pressure.

quay: A wharf.

race: Genetically distinctive people derived from Amerind, Austroloid, Caucasoid, Mongoloid, or Negroid stock. See also clan; ethnic group; tribe.

radioactive fallout: The precipitation of radioactive particles from clouds of debris produced by nuclear detonations, especially surface bursts that suck huge amounts of material into mushroom stems, after which winds aloft may waft a deadly mist over immense areas.

rain forest: Dark, dank, tropical woodlands where annual precipitation exceeds 100 inches (250 centimeters) and lofty evergreen trees form a continuous canopy that may contain two or more tiers. Little undergrowth exists except along streams and in clearings where sunlight reaches the forest floor. See also jungle.

reef: A chain of rocks, a ridge of sand, or a coral formation slightly submerged or nearly so which blocks or impedes passage between open ocean and beaches, even for flat-bottomed boats.

region: A large geographic area that is physically or culturally homogeneous. See also regional geography.

regional geography: A multidisciplinary field that subdivides Earth and space into such distinctive areas as Europe, Asia, and Africa south of the Sahara, then describes the attributes of each, with particular attention to political, military, economic, social, and other implications. Regional geography in a different vein addresses such homogeneous areas as mountains, deserts, and jungles. See also geography.

relative humidity: The actual amount of water vapor in the air compared with the greatest amount possible at the same temperature. Usually expressed as a percentage. See also absolute humidity; humidity.

relief: The irregularities of land surfaces and submarine topography; differences in elevation between adjacent terrain features. See also local relief.

right ascension: The celestial equivalent of longitude. The constellation Aires, against which spectators on Earth see the sun when it crosses Earth's equator (the vernal equinox), defines the prime meridian. Astronomers measure angular positions in space east from that celestial counterpart of Greenwich Observatory. See also declination.

riverine operations: Military activities along rivers and in wetlands. See also "brown water;" wetlands

Rome Plow: An armored bulldozer fitted with a blade designed to clear small trees and dense vegetation. Used extensively by U.S. Armed Forces in Vietnam.

runoff: Precipitation that does not sink into the ground, but flows over the surface into rivers and other streams.

savanna: Tropical or subtropical grasslands with scattered trees and drought-resistant plants.

sea line of communication (SLOC): Any maritime route that nations depend on for commercial or military purposes. See also line of communication.

seaport: A harbor that includes berthing, cargo-handling, storage, maintenance, and clearance facilities. See also harbor.

sea smoke: A phenomenon that occurs when very cold air over relatively warm open water produces steamy condensation that sometimes rises several hundred feet (100+ meters). See also arctic sea smoke.

semiarid: A region in which average annual precipitation measures between 10 and 20 inches (25-50 centimeters). See also desert; steppe.

set: The direction that ocean currents move. See also current; drift.

sight defilade: A position screened against or shielded from enemy observation. See also concealment; defilade.

slope: See grade; gradient.

soil trafficability: The capacity of surface materials to support cross-country movement by motor vehicles.

solar flares: Spectacular, pervasive outbursts of energy that emanate periodically from the sun, accompanied by high-speed protons that comprise a potentially lethal radiation hazard to any unshielded form of life in space. Intense and sudden ionospheric disturbances inflict fadeouts and other debilitating effects on long-range telecommunications. Major flares last from a few minutes to several hours.

space: The universe and all of its contents, except Earth and its atmosphere. See also circumterrestrial space; cislunar space; deep space; outer space.

spacecraft: Any manned or unmanned vehicle intended primarily for operations beyond Earth and its atmosphere.

space weather: Phenomena that occur 30 miles (50 kilometers) or more above Earth.

spring: A natural flow where the water table intersects Earth's surface. See also artesian spring; well.

spring tides: Tides about 20 percent greater than average arise twice a month when the sun reinforces lunar pull at the time of new and full moons and the Earth, sun, and moon are directly in line. See also neap tides; tide.

steppes: Vast, semiarid, treeless, grassy plains in European Russia and Central Asia. See also semiarid.

stratosphere: Atmosphere 10 to 20 miles (16 to 48 kilometers) above Earth's surface. Life support systems are essential. Temperatures decrease with altitude in lower layers, but inversions occur at the top, where maximum readings reach about 45 ⁰F (7.2 ⁰C).

swamp: A generic term for wetlands. See also bog; marsh.

swell: Long, low, parallel, crestless waves that continue almost indefinitely after motivating winds abate. See also wave.

tactical area of responsibility (TAOR): Any AOR below theater level. See also area of responsibility; theater.

taiga: Moist, subarctic, coniferous forests, mostly spruce and fir, the northern frontier of which touches tundra.

terracentric: A military mindset that emphasizes land power.

terrain: All physical and cultural geographical features within any given area.

territorial sea: A maritime area that includes air space and the seabed over which coastal countries exercise sovereignty. Such countries may claim rights up to 12 nautical miles from the baseline, according to the United Nations Convention on Law of the Sea. See also baseline.

theater: A regional area of responsibility, such as Western Europe, North Africa, and Southeast Asia. See also area of responsibility; region.

thermocline: A layer of increasingly colder, saltier ocean water that separates relatively light, seasonally-variable mixtures near the surface from a dense isothermal layer several thousand feet below. See also isothermal area.

thermosphere: Thin atmosphere 30-50 miles (48-80 kilometers) above Earth's surface, where tremendous inversions cause temperatures to increase dramatically. Peak readings near the top may reach 2,250 ⁰ F (1,250 ⁰ C). Diurnal variations probably are several hundred degrees.

tidal current: The alternating horizontal movement of water that rises and falls with tides. The direction in relatively open locations rotates continuously through 360 degrees diurnally or semi-diurnally. Local topography strongly influences tidal current characteristics in coastal waters. See also tide; tidewater.

tide: The rising and falling of oceans, seas, and large lakes twice daily in response to unequal gravitational attractions of the sun and moon. See also neap tide; spring tide; tidal current; tidewater.

tidewater: That portion of any river affected by the ebb and flow of tides. See also tide.

tombolo: A sand or gravel bar that connects an island to the mainland or another island.

topographical crest: The highest point on any slope. See also crest; military crest.

topography: The configuration of land or underwater surfaces, especially relief and other natural features. See also relief; terrain.

town plan: The current configuration of any city, town, village, or hamlet, which may or may not reflect a preconceived design.

trafficability: See soil trafficability.

tribe: A group of culturally and linguistically homogeneous people who occupy certain territory. See also clan.

troposphere: Atmosphere from Earth's surface to about 10 miles (16 kilometers) above the equator and half of that altitude near the North and South Poles. Most clouds, winds, precipitation, and other weather phenomena occur in this region.

tundra: An arctic or subarctic plain, level to undulating, treeless, with permanently frozen subsoil and a mucky surface that supports stunted plants such as mosses and lichens.

twilight: Periods of incomplete darkness before sunrise and after sunset. Durations vary from a few minutes to many hours, depending on latitude and season. See also Beginning of Morning Nautical Twilight; End of Evening Nautical Twilight.

urban area: Any city or built-up portion thereof. See also urbanization; urban sprawl.

ubanization: Any plot of land where population densities equal or exceed 1,000 persons per square mile (about 3 square kilometers). See also urban area; urban sprawl.

urban sprawl: The coalescence of several cities to form a contiguous metropolitan area many miles long and wide.

Van Allen belts: Two intense radiation layers trapped in Earth's magnetosphere from 45 degrees north to 45 degrees south latitude . The lower layer begins between 250 and 750 miles (400-1,200 kilometers) above Earth's surface and tops at 6,200 miles (9,655 kilometers). A low particle slot separates it from the upper layer, which terminates at 37,000-52,000 miles (59,550-83,685 kilometers), depending on solar activity. Protons are most prominent at 2,200 miles (3,550 kilometers). Electron flux peaks at approximately 9,900 miles (15,930 kilometers). Spacecraft need shielding to transit either Van Allen belt safely. See also magnetosphere.

visibility: The greatest distance at which observers with 20/20 eyesight can see and identify prominent objects unaided by binoculars or night vision devices.

visual flight rules (VFR): Air traffic control regulations that pertain when cloud ceilings, visibility, and other weather conditions are more favorable than specified minimums. See also Instrument Flight Rules.

wadi: The bed of a stream that dries up seasonally or during droughts (a term most commonly used in North Africa and the Middle East). Heavy rains commonly cause flash floods in such water courses. See also arroyo; intermittent stream.

watershed: See drainage basin.

water table: The upper limit of saturated soil, which may be on the surface or many feet (meters) below.

wave: Solid water that forms peaks and troughs above and below the normal surface of oceans, seas, and large lakes. Waves on open seas are generated in four ways: by winds that act on the surface; by changes in atmospheric pressure; by seismic disturbances such as earthquakes; and by tidal attractions of the sun and moon. See also wave period.

wave period: The time it takes one wave crest to succeed another.

weather: The condition of Earth's atmosphere at present and for the predictable future. See also climate; meterology; weather forecast.

weather forecast: Predicted atmospheric conditions at a point, along a route, or within a given area for a specified period of time. Reliability decreases as forecast periods increase. Predictions from 48 to 96 hours in the future are called "outlooks."

wetlands: Any swamp, bog, or marsh.

wharf: A structure built alongside, or at an angle to, the shore of a seaport or navigable inland waterway where ships and smaller craft receive and discharge cargo and passengers.

whiteout: A weather phenomenon that occurs when snow obliterates surface features, overcast eliminates shadows, and the horizon is invisible. Earth and sky seem inseparable.

wind chill: The effect of moving air on exposed flesh at any given temperature. High velocities produce low sensible temperatures.

wind shear: See-saw effects along boundaries between strong air currents that race in opposite directions above and below one another.

Contact Us
NDU Press Home Page
NDU Home Page
INSS Home Page

Last Update:  September 30, 2002