Representations of Earth

Vocabulary-style flashcards covering key concepts from the Representations of Earth lecture notes.

oblate spheroid

Earth’s shape caused by its rotation; bulges at the equator and is slightly flattened at the poles, deviating slightly from a perfect sphere.

cartography

The science and practice of map making and map design to communicate geographic information.

great circle

The largest circle possible on a sphere; the intersection with a plane that passes through Earth’s center; shortest route between two points.

small circle

Any circle on a sphere that does not pass through the sphere’s center; not the shortest route between two points.

latitude

Angular distance north or south of the equator, measured in degrees.

longitude

Angular distance east or west of the prime meridian, measured in degrees.

equator

0° latitude; the circle dividing Earth into the Northern and Southern Hemispheres; a great circle.

parallels

Lines of latitude that run east-west; evenly spaced; the equator is a great circle; others are small circles.

meridians

Lines of longitude that run north-south; converge at the poles and form great circles with their counterparts.

geographic grid

The coordinate grid of latitude and longitude used to locate any point on Earth.

prime meridian

0° longitude line, passing through Greenwich, England, used as the reference for longitude.

Greenwich Mean Time (GMT)

Worldwide time standard used as a reference for time zones (now often UTC).

decimal degrees

Coordinates expressed as decimal numbers rather than degrees/minutes/seconds; common in GPS/GIS.

International Date Line

Line opposite the prime meridian (roughly 180°) where the calendar date changes when crossed.

time zones

Standardized longitudinal divisions (about 15° each) used to set local times around the world.

GPS

Global Positioning System; satellite-based system that determines precise locations via triangulation.

GIS

Geographic Information System; computer system for storing, analyzing, and displaying geographic data in layers.

map projection

Method of transferring a curved Earth surface to a flat map, inevitably causing distortion.

planar projection

Projection onto a plane, often used for polar regions; can exaggerate some distortions elsewhere.

conic projection

Projection onto a cone, commonly used for mid-latitude regions; meridians become straight lines radiating toward the pole.

cylindrical projection

Projection onto a cylinder; meridians appear as straight parallel lines; often distorts high-latitude areas (e.g., Mercator).

Mercator projection

A cylindrical, conformal projection that preserves angles and directions but distorts area, especially near the poles.

conformal map

A map that preserves local shapes and angles; meridians and parallels cross at right angles.

equal-area map

A map that preserves area proportions; shapes may be distorted.

azimuthal projection

Projection with true directions from a central point; straight lines from center are true compass directions.

gnomonic projection

Planar projection where great circles appear as straight lines; extreme distortion elsewhere but useful for navigation.

compromise projection

Projection balancing distortions of area and shape; aims for an “accurate looking” global map (often interrupted as needed).

map basics

Essential map elements such as title, date, legend, scale, and direction.

legend

Map key explaining the symbols, colors, and shading used on the map.

scale

Relation between distances on a map and actual ground distances; expressed as verbal, RF, or graphic scales.

verbal scale

A written statement of scale (e.g., 1 cm = 1 km); can be altered by resizing the map.

representative fraction (RF) scale

A scale ratio without units (e.g., 1:63,360); same unit in numerator and denominator.

graphic scale

A bar or line scale showing distances on the map relative to real ground distances.

magnetic declination

Angle between true north and magnetic north at a location; varies by place and time.

isogonic map

Map showing lines of equal magnetic declination across regions.

azimuth

Direction measured clockwise in degrees from north (0° to 360°).

bearing

Direction expressed in quadrants (N, E, S, W) with degrees from a north/south baseline.

thematic map

Map focused on the spatial distribution of one feature or a related set of features.

discrete data

Data that occur only at specific places (points, lines, or areas) and are not everywhere.

continuous data

Data that exist everywhere within the study area and can be measured continuously.

isoline

Line connecting points with the same value (e.g., isotherms, isobars, isohyets, isobaths).

contour interval

Elevation difference between adjacent contour lines on a topographic map.

topographic map

Map showing elevation changes with contour lines to depict terrain.

contour line

Line on a map joining points of equal elevation.

digital elevation model (DEM)

Digital 3-D representation of terrain elevations.

vertical exaggeration

Increasing the vertical scale relative to horizontal to emphasize relief on a profile or 3-D view.

draping

Layering imagery over elevation data in a GIS to create a 3-D visualization.

remote sensing

Collection and interpretation of information about distant objects or environments via aerial or satellite imagery.

aerial photography

Photos taken from aircraft (oblique or vertical) used for mapping and interpretation.

digital image

Raster image composed of pixels; digital data representing brightness/color.

pixel

The smallest element of a digital image; has a location and a value.

spatial resolution

Ground area represented by each pixel; higher resolution means smaller ground area per pixel.

near-infrared (NIR)

Infrared wavelengths not visible to the eye; vegetation often appears bright red in false color images.

thermal infrared (TIR)

Infrared wavelengths that detect heat differences; used to map temperature patterns.

radar

Radio detecting and ranging; uses microwaves to create imagery that can penetrate clouds.

SLAR

Side-looking airborne radar; images terrain from the side of an aircraft for mapping.

lidar

Laser-based remote sensing that yields high-resolution elevation data and surface detail.

multispectral

Remote sensing method that captures data in multiple spectral bands for analysis.

color composite image

Combining three spectral bands into a single color image for analysis.