Projection Flashcards
(21 cards)
What defines Earth’s shape mathematically?
Semi-major (horizontal) and semi-minor (vertical) axes.
What is a geodetic datum?
Defines Earth’s size/shape + coordinate system origin/orientation.
Key difference between NAD83 and WGS84?
NAD83 uses Kansas reference point; WGS84 uses Earth’s mass center.
Main disadvantages of globes?
Only shows half Earth; difficult measurements; hard to transport.
What do map projections do?
Transform 3D Earth to 2D surface, always causing distortion.
Four types of projection distortion?
Shape (conformality), Area, Distance, Direction.
Which projection preserves shapes?
Conformal (e.g., Mercator / Lambert Conical).
Which preserves area sizes?
Equal-area/Equivalent (e.g., Mollweide).
Which preserves distance?
Equidistant (e.g., azimuthal equidistant)
Three projection surfaces?
Conic, Cylindrical, Planar.
Where does distortion occur least?
At tangent points/lines where surface touches globe.
How do secant lines help?
Create two distortion-free lines, reducing overall distortion.
Three projection aspects?
Normal (equator), Transverse (poles), Oblique (any angle).
Best projection for thematic maps?
Equal-area (e.g., Albers Conic).
Best for navigation?
Conformal (e.g., Mercator/Lambert Conic).
What do azimuthal projections preserve?
Directions from center point (e.g., Lambert Azimuthal).
HK1980 Grid origin coordinates?
800,000m N/E (artificial offset from 0).
How to choose a projection?
Consider purpose (area/distance/direction), distortion, and region size/location.
Geographic vs Cartesian systems?
Geographic uses lat/long (3D); Cartesian uses x/y axes (2D).
How are Cartesian coordinates structured?
4 quadrants with origin (0,0); locations as (x,y) pairs.
Example of Cartesian coordinates?
New York: (-74.04, 40.69) = (longitude, latitude).
