Study 3 Coordinate Systems and Reference Systems with 12 free online flashcards. Review key terms, definitions, and concepts with this interactive flashcard deck.
What does a coordinate reference system define?
A coordinate reference system (CRS) explains how coordinate values relate to locations on Earth. It combines a coordinate system with a datum or reference frame; a projected CRS also specifies a map projection.
How does a geographic coordinate system locate places?
A geographic coordinate system (GCS) locates places on a model of Earth using angles, usually latitude and longitude measured in degrees.
What does latitude measure?
Latitude measures north–south position relative to the equator.
How does the ground distance of one longitude degree vary?
A degree of longitude represents a shorter ground distance near the poles than near the equator.
How does a projected coordinate system represent locations?
A projected coordinate system (PCS) represents locations on a flat plane, typically with easting and northing measured in meters or feet.
Why does every map projection introduce distortion?
Flattening Earth's curved surface introduces distortion: every projection changes at least one property, such as area, shape, distance, or direction. No projection is best for every purpose.
Why is Web Mercator often unsuitable for measurement?
Web Mercator is widely used for online map display, but its area and distance distortions make it unsuitable for many measurement tasks.
What does a datum define?
A datum or geodetic reference frame defines how a mathematical model of Earth is positioned and oriented relative to Earth; it includes or is associated with a reference ellipsoid.
How does assigning a CRS differ from transforming data?
Assigning a CRS tells software what existing coordinate values mean without changing them. Transforming or projecting data calculates new coordinate values in a target CRS.
What does longitude measure?
Longitude measures east–west position relative to a reference meridian.
What property does an equal-area projection preserve?
An equal-area projection preserves area, making it useful for comparing the sizes of regions.
What does a conformal projection preserve, and what may it distort?
A conformal projection preserves local angles and shapes. It can be useful for some navigation and mapping tasks, but may distort area.