Mapping Glossary

B

base map
a map showing certain fundamental information on which can be compiled additional, specialized data.

C

compilation
production of a new map from existing maps, aerial photographs, and other sources.

concept map
a map-like illustration that shows relationships between concepts.

context
the interrelated conditions in which something exists.

D

dead reckoning
The estimation of a ship's position from the distance according to the ship's log and the course steered by the compass, with corrections for currents and other factors, but without astronomical observations.

digital mapping
the making of maps using computerized data and procedures.

distortion
the lack of proper proportion; directions, shapes, distances, and sizes of areas may be shown inaccurately.

E

electromagnetic spectrum
the range of wavelengths or frequencies of electromagnetic radiation including gamma rays, visible light, and the longest radio waves.

G

generalization
the simplification of data by eliminating unneeded detailed data.

Greenwich time
Mean solar time of the meridian of Greenwich, England, used by most navigators and adopted as the basis of standard time throughout the world.

grouping
the simplification of data by sorting data into similar sets.

I

image
likeness of an object or view; in remote sensing, a likeness produced without photography using an electronic spectral sensor.

isoline
a line through points of equal value.

L

landmark
Any prominent object on land that can be used in determining a location or direction.

latitude
Angular distance measured in degrees, minutes, and seconds north and south to the geographic poles from the equator.

layer
in digital cartography, map data on a common theme manipulated separately from other types of data.

longitude
Angular distance measured in degrees, minutes, and seconds 180 degrees east and west from the Prime Meridian, the imaginary north-south line through Greenwich, England.

M

magnetic compass
an instrument having a magnetic needle to indicate magnetic north.

map design
the choices made in creating a map; decisions are generally based on the maps purpose, intended audience, and characteristics of the spatial data.

mappa mundi
From two Latin words meaning tablecloth and world, a graphic or verbal representation of the world as understood in the Middle Ages in Europe.

marine chronometer
A portable timekeeper with a special mechanism for ensuring and adjusting its accuracy, for use in determining longitude at sea.

mosaic
a whole image or map made from parts from more than one source.

O

optics
the science that deals with light and closely associated phenomena.

orientation
alignment, usually in reference to points on the compass.

P

perspective
the appearance to the eye of objects in respect to their relative distance and position; the technique of representing the spatial relationship of objects as they might appear to the eye.

photogrammetry
The techniques used to obtain reliable measurements from photographs.

planetable
A device for plotting survey data directly from field observation. Consists of a drawing board on a tripod with a sighting instrument to measure and plot angles.

planisphere
A projection or representation of the whole or part of a sphere on a plane.

portolan chart
A type of sea chart common in the Middle Ages that was used for navigation at sea. Characterized by rhumb lines, or lines of constant compass heading, and the names of ports. From the Italian, portolano, a collection of sailing directions.

positional accuracy
the accuracy of the location of a point.

Q

qualitative
related to quality or kind.

quantitative
related to quantity, value, or amount.

S

scale
the relationship of the size of a feature on a map to its size in reality.

• bar scale
  scale shown by a line, which is labeled to represent a stated distance.

• representative fraction scale
  scale indicated by a ratio of one unit on the map to some number of the same units on the ground, for example 1/24,000.

• verbal scale
  scale indicated by a phrase such as "one inch represents one mile."

• large scale
  good for showing detail in small areas.

• small scale
  good for showing a general view of a large area.

R

remote sensing
the process of detecting and monitoring physical characteristics of an area by measuring its reflected and emitted radiation and without physically contacting the object.

S

sextant
An astronomical instrument for measuring angles, primarily altitudes of celestial bodies, to determine latitude.

spatial data
information pertaining to a place linked to coordinates or other positional information.

stereoscope
a device used to view overlapping photographs to obtain the mental impression of a three-dimensional image, or model.

surveying
The techniques used to make measurements in space to determine the relative positions of map features.

T

thematic map
a map designed to show information on a single topic.

theodolite
A precise surveying instrument having a telescopic sight for measuring horizontal and vertical angles.

triangulation
A method of surveying in which the stations are points on the ground at the vertices of a chain or network of triangles. The angles of the triangles are measured instrumentally and the sides are derived by computation from selected sides or bases, the lengths of which are obtained by direct measurement on the ground or by computation from other triangles.