definitions

Point-to-Point Correspondence

The idea that each point on Earth is transformed to a corresponding point on the map projection.

Continuity

Preservation of spatial proximity at all locations.

Graticule

A model of earth-centered coordinate system, most commonly latitude and longitude.

Pattern of Distortion

Illustrated through a diagram known as Tissot’s indicatrix.

Sinusoidal

A type of projection that is equal-area.

Robinson

A map projection based on a table of coordinates, not mathematical formulas.

Equidistant Conic

A projection used to portray area near, but not overlapping, the Equator.

Albers Equal Area Conic

A projection that distorts scale and distance.

Lambert Conformal Conic

A projection that preserves true directions in limited areas.

Conic projections

Includes equidistant, Albers equal area, and Lambert conformal.

Cylindrical projection

Includes Equirectangular, Mercator, Gall’s Stereographic Cylindrical, Peters Projection, and Transverse Mercator.

Transverse Mercator

A projection used to portray areas with larger north-south than east-west extent.

Peters Projection

A special case of Gall’s equal-area projection.

Gall’s Stereographic Cylindrical

A secant projection.

Mercator

A projection used for navigational maps and charts.

Equirectangular

Also called an equidistant cylindrical projection.

Plane (azimuthal)

Commonly used for mapping polar regions; good for areas with about equal north-south and east-west extents.

Conic

Great for representing mid-latitude regions in either hemisphere.

Cylindrical

Good for maps of the entire Earth.

Plane

Includes Orthographic, Stereographic, Gnomonic, Azimuthal Equidistant, Lambert Azimuthal Equal Area.

Stereographic

Good for navigating polar regions.

Developable surface

A flat surface that Earth’s features are projected onto.

Equivalent projections

Preserves the relative size of regions on the map.

Conformal projections

Preserves angles on globe and, ultimately, the shape.

Equidistant projections

Preserve distance relations.

Datums

A collection of very accurate control points.

Geodesy

The science of measuring and modeling the Earth in 3D.

Ellipsoid

A mathematical model of Earth with major and minor axes.

Flattening ratio

The rate at which the ellipsoid flattens as one approaches the poles.

Horizontal datum

Ellipsoid plus flattening ratio, serving as a basis for fitting the ellipsoid model to Earth’s surface.

Vertical datum

The basis for measuring elevation and the 0-reference for elevation.

Mean Sea Level (MSL)

Average of all low and high tides at a particular location over a metonic cycle.

Spatial

Refers to location.

Representation

Something that stands for or portrays something else; likeness; simplified model.

Graphically

Drawn or capable of being drawn, with a unique arrangement of features; encompasses diversity.

Communicate

The map’s ultimate purpose is to convey information to the reader.

Topographic

Reference maps.

Thematic

Themed maps.

Spatialization

The origins of language and growth of spatial consciousness in humans are closely interrelated.

Primary source

Gathered first-hand, collected in the environment.

Secondary source

Derived from primary data, such as focus groups or surveys.

Tertiary source

Derived from secondary data, such as websites or reports.

Types of thematic maps

Include themed maps, such as population maps represented with dots.

Types of topographic maps

Traditional reference maps or atlases, including globes.

Absolute relief mapping

Shows precise elevation information.

Relative relief methods

Shows various landforms and general impressions of relative height.

Contours

Lines of equal elevation above a datum.

Parcels/tracts

Areas that imply landownership or land use.

Lot

A special type of parcel within a subdivision, recorded on a map.

Plat

A map drawn to scale that shows the lots.

Platted Subdivision

Mapped subdivision showing subdivided lots.

Cadastral system

The means by which property ownership is recorded, boundary lines are drawn, and land parcels are delineated.