map projection properties

Question 1

Refrence globe

Answer 1

a model of the Earth at some chosen scale

Question 2

Developable surface

Answer 2

a mathematically definable surface onto which the land masses and graticule are projected from the reference globe

Question 3

List the 3 developable surfaces/ classes

Answer 3

cone - concical class
plane - planar class
cylinder - cylindrical class

Question 4

Case

Answer 4

tangent
secant

Question 5

Aspects

Answer 5

polar
equatorial
obligue

Question 6

why does distortion occur?

Answer 6

There isn’t a constant scale on the earth’s surface because it is obligate ellipsoid. Distortion is inevitable.

Question 7

scale factor

Answer 7

local scale / princicple scale

Question 8

Tissot’s indicatrix

Answer 8

Provides a visual means of showing how distortion varies at point locations across a projection.
A quantitative analysis of distortion that describes the amount and type of distortion that occurs at points across the map

Question 9

Azimuthal projections

Answer 9

preserve directions, only from centre of map to any other point along a great circle.
e.g Lambert equivalent

Question 10

conformal projections

Answer 10

preserve angular relationships around a point
e.g Lambert conformal conic projection

Question 11

Compromise projections

Answer 11

preserve no specific property, but rather strike a balance among various projection properties.
SF can be manipulated so that the extreme angular and aerial distortion found on equivalent and conformal.
e.g Robinson projection

Question 12

equidistant projections

Answer 12

Preserving the principle scale between 2 points on a map. Distance can only be preserved in one direction.
e.g equirectangular cylindrical and Euler equidistant conic

Question 13

What is distortion?

Answer 13

is the alteration of the size of the earth’s landmasses and the
arrangement of the earth’s graticule when they are projected to a 2D flat map

Question 14

VIsual approach to distortion

Answer 14

visual comparison of the sizes of landmasses and the arrangement of the graticule on a projected map

Question 15

Scale factor to analyse distortion

Answer 15

SF=is a numerical assessment of how the map scale at a location on the map compares with the principal map scale.
Compute how much deviation exists between the local scale and the principal scale at any location on a given projection. Variation in SF can be used to
quantify the distortion on the map for
different locations

Question 16

Tissots indicatrix to analyse distortion

Answer 16

based on a unit circle
r-1.0, where all spatial relationships are preserved.
a=b=1
when a=b there is no distortion
when a=/b but a=1 then there is angular distortion
when a=b but a=/ 1 then aerial distortion takes place
when a=/b and a=/1 angular and aerial distortion occurs

Question 17

list the 4 projection properties

Answer 17

Areas
angles
distances
direction

Question 18

equivalent projections

Answer 18

preserves areas
e.g Albers equal area