Representations of Earth Vocabulary

A set of vocabulary flashcards based on lecture notes covering geography, mapping projections, coordinates, GIS, and remote sensing.

Cartography

The science and profession of mapmaking, focused on designing maps and globes to ensure spatial information is accurate and effectively presented.

Oblate spheroid

The shape of Earth, which bulges outward at the equator and is slightly flattened at the polar regions due to centrifugal force from daily rotation.

Great circle

An imaginary circle drawn in any direction on Earth's surface whose plane passes through the center of Earth, dividing it into two equal halves or hemispheres.

Small circle

Any circle on Earth's surface whose plane does not pass through the center of Earth and does not divide the planet into equal halves.

Latitude

The angular distance measured in degrees north or south of the equator, ranging from $0^\text{o}$ at the equator to $90^\text{o}\text{N}$ or $90^\text{o}\text{S}$ at the poles.

Longitude

The angular distance measured in degrees east or west of the prime meridian, extending to a maximum of $180^\text{o}$.

Prime meridian

The arbitrarily established $0^\text{o}$ longitude reference line passing through Greenwich, England, used as the starting line for measuring east and west angular distance.

Geographic grid

The global system of imaginary intersecting lines, comprising parallels of latitude and meridians of longitude, used to reference locations on Earth.

Parallels

East-west lines marking latitude that circle the globe, are evenly spaced, and run parallel to the equator and each other.

Meridians

North-south lines of longitude that converge at the poles and measure distances east and west of the prime meridian.

International Date Line

A line that generally follows the $180^\text{th}$ meridian where travelers cross to turn the calendar back a full day (traveling east) or forward a full day (traveling west).

U.S. Public Lands Survey System

A land-partitioning grid system (also called the Township and Range System) used in much of the United States based on perpendicular principal meridians and base lines.

Township

A nearly square plot of land $6\text{ miles}$ on a side ($36\text{ sq mi}$) in the U.S. Public Lands Survey System, located by its tier position relative to a base line and range relative to a principal meridian.

Section

A $1\text{ square mile}$ ($640\text{ acres}$) parcel of land within a township, designated by numbers from $1$ to $36$.

Global Positioning System (GPS)

A high-tech system for determining locations on Earth by calculating distances using radio signals transmitted from a satellite network orbiting $17,700\text{ km}$ above Earth through triangulation.

Map projection

The mathematical transfer of the spherical geographic grid onto a flat surface, which inherently distorts shape, area, distance, or direction.

Mercator projection

A mathematically adjusted cylindrical map projection on which meridians appear as parallel lines and straight lines represent rhumb lines, resulting in high-latitude area distortion.

Rhumb line

A line of constant compass heading, which appears as a straight line on a Mercator projection.

Equal-area map

A map projection that preserves correct proportional size relationships among areas across the map, at the cost of distorting shapes.

Conformal map

A map projection that preserves the correct shapes of geographic features by having meridians and parallels cross at right angles ($90^\text{o}$), though area sizes are distorted.

Compromise projection

A world map projection, such as the Robinson projection, that balances distortion to show both area and shape reasonably well without being strictly conformal or equal-area.

Verbal scale

A map scale stated in words comparing a map measurement to an Earth distance, such as "$1\text{ inch}$ to $1\text{ mile}$".

Representative fraction (RF) scale

A unitless ratio or fraction representing the relationship between a distance on a map and actual distance on the ground using identical units, such as $1:63,360$.

Graphic scale

A line or bar device marked with map distances proportional to actual ground distances, which remains accurate even if the map is resized.

Magnetic declination

The angular difference between magnetic north (where a compass needle points) and true geographic north.

Thematic map

A map designed to focus attention on the spatial extent and distribution of one specific feature or a set of related features.

Discrete data

Spatial data representing features that are present at specific locations but do not exist everywhere, represented using point, line, or area symbols.

Continuous data

Spatial data representing measurable numerical values that exist everywhere across a given area, such as elevation, temperature, or air pressure.

Isoline

A line on a map connecting points with the same numerical value of a continuous variable.

Topographic map

A map portraying land surface elevational information using contour lines alongside natural and cultural features.

Contour interval

The constant elevation difference between adjacent contour lines on a topographic map.

Topographic profile

A side-view diagram illustrating the shape and elevation changes of a land surface over distance along a transect line.

Gradient

The rate of change in a variable per unit of horizontal distance, visually reflected by the spacing of isolines on a map.

Geographic Information System (GIS)

A computer-based system that stores geographic databases, supports spatial analysis, and combines multiple digital thematic map layers.

Digital Elevation Model (DEM)

A computer-generated grid dataset or three-dimensional representation of elevation data.

Vertical exaggeration

A technique that stretches the vertical scale relative to the horizontal scale in profiles or block diagrams to emphasize subtle terrain variations.

Remote sensing

The collection of information and data about distant objects or environments from aerial photographs or satellite imagery.

Pixel

Short for picture element; the smallest resolved area unit in a digital image.

Spatial resolution

A measure of the ground area represented by each pixel in a digital image.

Near-infrared (NIR)

Light energy at wavelengths slightly longer than visible light, which cuts through atmospheric haze and portrays healthy vegetation as bright red in false-color imagery.

Thermal infrared (TIR)

Remote sensing energy that records radiation patterns of heat and temperature day or night.

Radar

A remote sensing system (radio detection and ranging) that transmits radio waves and measures reflected signals to map surface features or track precipitation.

Sonar

A system (sound navigation and ranging) that uses reflected sound waves to probe ocean depths and map seafloor topography.

Multispectral remote sensing

Remote sensing technology that simultaneously captures and compares images across multiple energy wavelengths.