Ch 3: Scales and Projections

Question 1

scales

Answer 1

refer to how map units relate to real world units

Question 2

projections

Answer 2

deal with the methods and challenges around turning a 3D earth into a 2D map

Question 3

Representative fraction

Answer 3

Representative fraction → the most commonly used measure of map scale, where map scale is shown as a ratio

Question 4

Graphic scale

Answer 4

scale bars are graphical representations of distance on a map

Question 5

Verbal description

Answer 5

→ e.g. “one inch represents one km”

Question 6

extent of a map

Answer 6

The extent of a map describes the area visible on the map
Extent is like describing the region to which the map is zoomed
E.g. extent of a map is national

Question 7

resolution

Answer 7

resolution describes the smallest unit that is mapped
-e.g. the state

Question 8

coordinates

Answer 8

Locations on the earth’s surface are measured in terms of coordinates, a set of 2 or more numbers that specifies a location in relation to some reference system
Simplest system is a Cartesian coordinate system, a grid forms by putting together two measurement scales (x and y)

Question 9

geographic coordinate system

Answer 9

Geographic coordinate system is designed specifically to define positions on the Earth’s roughly-spherical surface

Used an east-west scale (longitude) and the International Date Line
Opposite of IDL is the prime meridian (line of longitude defined as 0 degrees)
North-south scale (latitude) ranges from north to south
Longitude specifies positions East and West and latitude specifies positions
At higher latitudes, the length of parallels decreases to zero
Lines of longitude are not parallel but converge toward the poles

Question 10

longitude

Answer 10

positions east and west

Question 11

latitude

Answer 11

positions north and south

Question 12

are lines of longitude parallel

Answer 12

Lines of longitude are not parallel but converge toward the poles

Question 13

projection

Answer 13

Map projection refers to both the process and product of transforming spatial coordinates on a 3D sphere to a 2D plane
Most projections transform part of the globe to one of three “developable” surfaces, so called because they are flat or can be made flat: plane, cone, and cylinder
The resultant projections are called planar, conical, and cylindrical
We use developable surfaces because they eliminate tearing, although they will produce shearing and compression

Question 14

tangent point/line

Answer 14

The place where the developable surface touches the globe is known as the tangent point/line
Maps will most accurately represent objects on the globe at these tangent points or line, with distortion increasing as you move farther away due to shearing and compression
It is for this reason that cylinders are often used for areas near the equator, cones used to map the mid-latitudes, and planes used for polar regions.

Question 15

how do projections distort features?

Answer 15

Projections must distort features on the surface of the globe during the process of making them flat because projection involves shearing, tearing, and compression
Since no projection can preserve all properties, it is up to the map maker to know which properties are most important for their purpose and to choose an appropriate projection

Question 16

conformal projections

Answer 16

Conformal projections preserve shape and angle, but distort area in the process

-For example, with the Mercator projection, the shapes of coastlines are accurate on all parts of the map, but countries near the poles appear much larger relative to countries near the equator than they actually are

Question 17

when should conformal projections be used

Answer 17

if main purpose of map involves measuring angles or representing the shapes of features
Useful for navigation, topography(elevation) and weather maps
-used as basis for large scale surveying and mapping

Question 18

equal area projection

Answer 18

the size of any area on the map is in true proportion to its size on Earth
Countries shapes many appear to be squished or stretched compared to what they look like on a globe but their land area will be accurate relative to other land masses
E.g. Gall-Peters projection, the shape of Greenland is significantly altered, but the size of its area is correct in comparison to Africa

Question 19

what are equal area projections important for

Answer 19

This type of projection is important for quantitative thematic data, especially in mapping density (an attribute over an area)

-For example, it would be useful in comparing the density of Syrian refugees in the Middle East or the amount of cropland in production.

Equal-area projections are preferred for small-scale thematic mapping, especially when map users are expected to compare sizes of area features like countries and continents

Question 20

what gets distorted on equal area projection

Answer 20

The ellipses maintain the correct proportions in the sizes of areas on the globe but that their shapes are distorted

Question 21

equidistant projections

Answer 21

Equidistant projections preserve distance
Equidistant maps are able, however, to preserve distances along a few clearly specified lines
For example, on the Azimuthal Equidistant projection, all points are the proportionally correct distance and direction from the center point

Question 22

what are equidistant projections used for

Answer 22

This type of projection would be useful visualizing airplane flight paths from one city to several other cities or in mapping an earthquake epicenter

Question 23

what gets distorted on an equidistant projection

Answer 23

Azimuthal projections preserve distance at the cost of distorting shape and area to some extent
The flag of the United Nations contains an example of a polar azimuthal equidistant projection

Question 24

Compromise, Interrupted and Artistic Projections (Robinson projections)

Answer 24

Don’t preserve a specific property but seek a compromise that minimizes distortion of all kinds, as with the Robinson projection, which is often used for small-scale thematic maps of the world
Interrupted projections such as the interrupted Goode Homolosine projection represent the earth in lobes, reducing the amount of shape and area distortion near the poles

Question 25

Compromise, Interrupted and Artistic Projections (Robinson projections) use

Answer 25

The projection was developed in 1923 by John Paul Goode to provide an alternative to the Mercator projection for portraying global areal relationships

Question 26

robinson distortion

Answer 26

The interrupted goode homolosine preserves area (equal-area or equivalent) but doesn’t preserve shape

Question 27

map scale shown as _____

Answer 27

ratio

Question 28

small scale map

Answer 28

ratio between the map and the world is smaller
-map shows LESS detail

Question 29

large scale map

Answer 29

the ratio between the map and the world is larger
-map shows MORE detail

Question 30

extent

Answer 30

area of the earth that’s visible on the map

Question 31

resolution

Answer 31

the smallest unit being mapped

e.g. countries and extent is continent

Question 32

developable surfaces

Answer 32

surfaces (plane, cone, cylinder) that the globe is transformed on to

Question 33

tangent point

Answer 33

place where the developable surface touches the globe
-maps will be MOST accurate at these points

Question 34

compromise projection distortion

Answer 34

projections that strike a balance between distortion of different map properties

Question 35

interrupted projection distortion

Answer 35

projections that tear the earth in strategic places to reduce shape and area distortion, but massively distort distances

Question 36

artistic projection distortion

Answer 36

projections that are aesthetically pleasing, but not intended for navigation or data visualization