Essential Geographic Definitions
Altitude
In geography, altitude is the vertical distance of a point on Earth relative to mean sea level (MSL). This contrasts with height, the vertical distance between two points on the surface, and flight level, the standard pressure altitude measured by an altimeter above 20,000 feet MSL.
Archipelago
An archipelago is a chain or group of islands. These islands are typically located in open water, less commonly near large landmasses. They often have volcanic origins, sometimes forming ridges or hotspots. Other processes like erosion and sedimentation also contribute to their formation.
Cordillera
A cordillera is a sequence of interconnected mountains, usually originating from the Alpine Orogeny. It extends across a vast territory and consists of large folds or creases and interleaving blocks. This occurs in geosynclines, elongated areas around continental edges, where thick sediment accumulates. Lateral thrust compresses these materials, leading to folds and mountain range formation. Examples include the Alps, Himalayas, and Andes.
Sedimentary Basin
A sedimentary basin is a significant accumulation of sediments resulting from Earth’s surface erosion.
Equinox
An equinox occurs twice yearly when day and night are equal in duration worldwide. Derived from Latin, it means “equal night.” During equinoxes, the sun lies in the Earth’s equatorial plane, reaching the zenith. The sun’s declination parallel and the celestial equator align.
Map Scale
Map scale is the ratio between map dimensions and actual surface dimensions. For example, a 1:100,000 scale means one inch on the map represents one real mile (100,000 times). Larger areas require smaller scales. Spanish topographic maps often use a 1:50,000 scale.
Geological Fault
A geological fault is a discontinuity in Earth’s surface rocks caused by fracturing. The rupture zone, a well-defined surface called the fault plane, forms alongside a tangential landslide of rocks. Sudden, abrupt fault activity can trigger earthquakes.
Glacial Lake
A glacial lake occupies a depression created by glacial erosion. Proglacial lakes form from glacial moraine melt, while other glacial lakes form behind moraines. Current glacial lakes result from intense Pleistocene climatic and geological glacier dynamics.
Geographic Latitude
Geographic latitude is the angular distance between the equator and a specific point on Earth, measured along the point’s meridian. It’s measured in degrees (°) from 0 to 90 and can be represented by indicating the hemisphere (North/South) or using positive values for North and negative for South (+/-). For example, 10°N can be +10° and 10°S can be -10°.
Coast
The coast is the strip between the highest and lowest tide lines. The littoral refers to cracks and fissures created by waves hitting sea cliffs. The sea’s force can erode rocks, causing collapses and holes through which water flows during high tide.
Geographic Longitude
In mapping, longitude is the angular distance between a point and the prime meridian (0°), measured from Earth’s center. It’s measured in degrees (°). It can be expressed from 0° to 360° eastward from the prime meridian, from 0° to 180° indicating the hemisphere (East/West), or from 0° to 180° using positive values for East and negative for West (+/-).
Topographic Map
A topographic map represents, usually partially, land surface relief at a defined scale. Unlike other maps, they depict large areas (provinces, regions, countries, or the world). Contours reflect the Earth’s surface shape. Colors, symbols, and auxiliary lines indicate mountains, valleys, rivers, hills, and other features. They also include human constructions like towns, roads, bridges, dams, power lines, and places.
Meridian
Meridians are imaginary circles on the celestial sphere passing through the poles. They determine time, year, etc. By extension, they’re great circles through any sphere or spheroid’s poles. Observers on the same meridian share the same time. When the sun is at its highest point, it indicates south (midday).
Plateau
A plateau is a large, elevated plain formed by tectonic forces or erosion. Tectonic forces acting on horizontal strata can uplift an area, maintaining its horizontal nature but at a higher elevation. Erosion can isolate and elevate areas of resistant materials. Underwater plateaus exist and can form from collapsed or flooded emerged plains.
Karst Morphology
Karst morphology describes the shaping of regions by limestone dissolution. Limestone, though hard, is water-soluble. This process is favored by dense fracture networks.
West
West refers to the direction of the setting sun. It broadly represents a set of cultures. The “Western World” can narrowly refer to medieval Western Europe or broadly encompass Greco-Roman culture and even Mesopotamian cultures like Sumerian and Ancient Egyptian.
Oriental/East
East refers to the direction of the rising sun. It extends to regions in that direction. In “Western” culture, it often refers to Asia, conventionally divided into the Middle East, Near East, and Far East. Languages in the East belong to various families, including Indo-European, Afro-Asian, and Altaic. Arabic, Farsi (Persian), and Turkish are commonly spoken.
Geographic Parallel
A geographic parallel is a circle formed by intersecting the celestial sphere with a plane perpendicular to Earth’s rotation axis. Longitude, measured east or west from the prime meridian (Greenwich), is determined along parallels. Unlike meridians, parallels are not great circles (except the equator) and don’t contain Earth’s center. Latitude, the angle between a meridian and the equator, is expressed as North or South. Meridians and parallels form the geographic coordinate system.
Peneplane
A peneplane is a vast, nearly uniform plain with slight unevenness, resulting from prolonged erosion and watershed coalescence. It comprises low-slope troughs and watersheds with residual reliefs along the river basin. It represents the last stage of the geographical cycle driven by water management.
Peninsula
A peninsula is a land area surrounded by water except for a narrow isthmus connecting it to a larger landmass. Some are considered “almost islands” due to their small size relative to the connected continent.
Continental Shelf
The continental shelf is the extended perimeter of each continent, covered by relatively shallow seas during interglacial periods. It starts at the coast and ends at the continental slope. Beyond the slope lie the continental rise and the abyssal plain.
Alpine Relief
Alpine relief results from Tertiary Alpine folding. Soft, secondary sediments folded, while hard, older materials broke. Examples include the Pyrenees and Betic Cordilleras. This landscape features abrupt, vigorous reliefs, revealing glacial erosion. It formed on plastic materials like secondary limestone.
Karst Landforms
Karst landforms are characteristic of limestone areas, typically in cold, humid regions. They develop on massive limestone rock, characterized by dissolution processes. Key features include sinkholes and dolines externally, and caves internally.
Hercynian Relief
Hercynian relief results from the Paleozoic Hercynian folding. Remnants of these folded mountains are partially faulted and metamorphosed. Examples in Spain include the Galician Massif and Extremadura peneplane. They exhibit soft, rounded forms due to their age and steady erosion. Their materials are metamorphic.
North
North, or Septentrion, is the cardinal point indicating the direction towards the North Pole along a meridian. It’s opposite South. In the northern hemisphere, it corresponds to the point on the horizon perpendicular to the North Star. Northern locations are called northern or boreal.
Solstice
Solstices occur when the sun reaches its highest or lowest point relative to the Earth’s equator. The summer solstice (around June 20-21) marks the sun’s zenith over the Tropic of Cancer, while the winter solstice (around December 22-23) marks its zenith over the Tropic of Capricorn.
Stream
A stream is a watercourse in mountainous areas with steep slopes and irregular flow, possessing high erosive capacity. It’s used in hydrography, geomorphology, and physical geography, often synonymously with ravine, though the latter relates more to the stream bed.
Glacial Valley
Glacial valleys, also called glacial troughs or U-shaped valleys, are formed by glacial erosion between mountain areas. They result from the movement of large glaciers, which are rivers of ice originating from cirques.
Base
Bases are plains and plateaus formed in the Paleozoic era due to erosion of mountain ranges from the Hercynian orogeny. They consist of crystalline rocks forming the relief’s foundation. These rigid, siliceous Paleozoic rocks (slate, granite, etc.) break rather than fold under orogenic thrust.