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Y3 T2 Geography 322 > Lecture 4 > Flashcards

Lecture 4 Flashcards

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1
Q

georeferencing

A

the general ability to locate feature accurately in geographic space is known as georeferencing

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2
Q

Geodesy

A

▪ Earth is an irregularly shaped sphere-type object, and to make it easier to work with, we define a datum, a reference or foundation surface against which accurate position measurements can be made
http://www.nanaimo.ca/assets/Departments/Fire~Rescue/Images/IMG_2488.jpg
▪Typically, when we discuss elevation, we reference sea-level, a form of datum
▪ but we need to identify a datum that works in all directions:
▪ x–> east-west
▪ y –> north-south
▪ z –> elevation

due to Earth’s rotation around it’s axis, Earth bulges slightly at the equator and is relatively flat at the poles

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3
Q

Earths shape is known as an oblate _____ or ________

A

spheroid, ellipsoid

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4
Q

the _________________ is the currently accepted ellipsoid – it is the one that the Global Positioning System (GPS) is based on

A

World Geodetic System 1984 (WGS84)

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5
Q

if the ellipsoid defines the ________ shape of Earth, the geoid defines the ________ shape

A

horizontal

vertical

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6
Q

Geoid

A

▪ strictly defined, the geoid is the equipotential surface of Earth’s gravity field
▪ think of the geoid as the shape of Earth if the oceans were allowed to flow freely under the continents to create a single, undisturbed global sea level covering the entire planet

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7
Q

Geoid and Ellipsoid

A

the geoid and ellipsoid are different representations of Earth’s shape, and from these we are able to generate the most accurate Earth positional information
▪ in some places, the ellipsoid and geoid coincide, but in others they may differ –the difference is known as geoid separation

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8
Q

Geoid Seperation

A

difference between geoid and ellipsoid

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9
Q

Horizontal Datum

Vertical Datum

A

▪ a collection of points on Earth that have been identified according to their precise northerly or southerly location (latitude) and easterly or westerly location (longitude)
-currently, the North American Datum 1983 is the most commonly used datum in Canada and the US, although older data products may be related to a different datum

▪a collection of spatially distributed points on Earth with known heights either above or below mean sea level
-in coastal areas, sea level is determined by a tide gauge; for inland areas, sea level is determined by the shape of the geoid

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10
Q

the Canadian Spatial Reference System (CSRS) had adopted the __________________ as its horizontal datum

A

North American Datum of 1983 (NAD83)

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11
Q

Geodesy Active Vs. Passive System

A

▪ passive system: traditional system based on precisely located ground control points

▪ active system: highly precise network of orbital sensors

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12
Q

Today the Canadian Geodetic Vertical Datum is the…

A

CGVD2013 is used and is based entirely on the geoid

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13
Q

Define Coordinate System

A

a coordinate system is a framework by which positions are measured and computed on a map

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14
Q

Cartersian Coordinates

A

▪ Cartesian coordinate system assigns two coordinates (x and y) to every point on a flat surface
▪ these coordinates represent a distance from an origin in the x and the y direction
▪ typically, the origin is in the middle, allowing for both positive and negative coordinates, and results in a quadrant arrangement
▪ to avoid negative values, some coordinate systems use false eastings (x) and false northings (y

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15
Q

parallels of latitude are always equally spaced, and 1° of latitude is about ___ km along the curvature of Earth’s surface anywhere on Earth

A

111

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16
Q

1 degree longitude= at 52 degrees

A 
1°𝑙𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑒 = 111 × cos (𝑙𝑎𝑡𝑖𝑡𝑢𝑑𝑒)
1°𝑙𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑒 = 111 × cos (52.13118) 
1°𝑙𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑒 = 111 × 0.613856 
1°𝑙𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑒 = 68.138km
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17
Q

Globe

A

only a globe can reflect the true shape of earth

-a globe depicts true shapes, directions, distances, and areas

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18
Q

Great Circles

A

great circles: a circle formed on the surface of a globe by a plane that passes through the centre of the sphere
-the arc of a great circle marks the shortest distance between two points across the surface of Earth

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19
Q

map projection

A

a map projection is a systematic transformation of the 3 dimensional Earth into a 2dimensional flat map
▪ there are many kinds of map projections, but all involve the transfer of the distinctive global patterns of parallels of latitude and meridians of longitude onto a developable surface (eg, plane, cone, or cylinder)

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20
Q

3 main types of map projections

A
  1. Planar(orothographic)
    - good for looking at poles
  2. conical(perspective conical)
    - used often to look at N.A
  3. cylindrical(Mercator)
    - world
21
Q

A projected map will always be deficient in at least one of these: 4

A

▪ true directions ▪ true distances ▪ true areas ▪ true shapes

22
Q

a map is ________ when at any point on the map the scale is the same in every direction, such that meridians and parallels intersect at right angles – this preserves the true shape of features, although the size will be distorted

A

conformal

23
Q

▪a map is __________ if every part of the map, as well as the map as a whole, has the same area as the corresponding part on Earth, at the same reduced scale

A

equal-area/equivalent
ex: goodes

▪ no map can be both conformal and equal-area

24
Q

T OR F

no map can be both conformal and equal-area

A

T

25
Q

a map is ____________ if it shows true distances only from the centre of the projection or along a special set of lines

A

Equidistant

▪ eg, an equidistant map with Saskatoon at the centre will show the true distance from Saskatoon to Regina, and from Saskatoon to Prince Albert, but not from Regina to Prince Albert
▪ no map can be both equal-area and equidistant

26
Q

___________ projection correctly represent selected angular relationships

A

conformal

ex: Lambert azimuthal equal-area map

27
Q

tangent

A

if the globe touches the surface at a single point, it is called tangent to the surface

28
Q

secant

A

if the globe intersects the surface, it is called secant to the surface

29
Q

any straight line on the mercator map is a _____ line

A

rhumb– not necessarily the shortest distance, but the correct direction
which is why it is used for navigation

30
Q

Mercator maps are _______

A

conformal

to maintain conformality, parallels are unequally spaced with increasing separations away from the equator

31
Q

Universal Transverse Mercator

A

Universal Transverse Mercator: made like a Mercator projection, but the developable surface is rotated 90° so that it is tangent to a meridian instead of a parallel

▪ extensive use of the Cartesian-based UTM coordinate system, composed of 60 zones, each 6° of longitude wide, with both north and south zones
▪ each zone has a central meridian, and false eastings; the equator is the north-south reference line
▪ useful for mapping large areas that are mainly north-south in extent

32
Q

UTM is best for ______ locations

A

small

-preferably with N-S positioning

33
Q

Mollweide map projection

A

▪ Mollweide: created in 1805, the equator is a straight horizontal line perpendicular to a central meridian that is ½ its length; all other meridians are equally-spaced arcs
▪ equal-area projection designed to inscribe Earth onto a 2:1 ellipse
▪ shapes are extremely distorted though, especially towards the edges of the map, therefore it is not conformal
▪ also known as a homolographic map, because the areas between parallels on the map are the same as reality
.very popular for making world maps

  • this one is more for midlatitudes
  • equal area map
34
Q

gnomonic azimuthal

A

.useful for finding the shortest route between points
-stretching happening at lower latitudes
-good for polar regions
▪ accurate at the centre point, increasing distortion toward the edge of the map

35
Q

stereographic azimuthal

A

▪ can show a greater extent than the gnomonic azimuthal, but cannot show both hemispheres entirely
▪ the only azimuthal projection that preserves true angles and local shapes
▪ often used to map large continent-scale areas of similar extent in all directions

36
Q

Orthographic azimuthal

A

▪ commonly used to display Earth, the moon, and other planets as if the viewer were infinitely far away in outer space
▪ closely resembles a 3-dimensional view of the globe

37
Q

Lambert Azimuthal Equal-Area

A

▪ best suited for regions extending equally in all directions from a standard point of tangent, which can be anywhere
▪ areas on the map are in their true proportion to the same areas on Earth
▪ directions are true only from the standard point of tangency
▪ the scale decreases gradually away from the standard point of tangency
▪ any straight line drawn through the standard point is a great circle
▪ the map is equal-area but not conformal or equidistant

.the distortion of shape increases away from the standard point of tangency

POSSIBLY TH BEST FOR REPRESENTING CANADA

38
Q

Azimuthal equidistant maps

A

are commonly used in aviation
▪ distances and directions to all places are true, but only from the standard point of tangency
▪ distances are true between points along a straight line, provided that line passes through the standard point of tangency
▪ commonly shown from a polar perspective, although oblique perspective are commonly used for world and continental-scale maps

distortion is 0 at the standard parallel and increases away

39
Q

Conic Map Projections

A

▪ conic projections are mathematically projected onto a cone-shaped developable surface
▪ the cone can be tangent or secant to the globe; if tangent, there is one standard parallel, if secant, there are two standard parallels

40
Q

Albers equal-area conic

A

is ideal for mapping large areas that are mainly east-west orientation

▪ this projection is not conformal or equidistant, but areas are maintained
▪ distances and the scale are true only along the standard parallel(s), but are reasonably accurate within a limited range of the standard parallel(s)
▪ adjacent Albers maps can be edge-matched only if they share the same scale and the same standard parallel(s

41
Q

Lambert conformal conic

A

is one of the most commonly used projections at a wide range of scales
▪ it is secant at two standard parallels
▪ although it looks like the Albers equalarea projection, the graticule is spaced differently
▪ best for mapping features that lie in an east-west orientation
▪ not equal-area or equidistant, but distance and directions are relatively accurate close to the standard parallels
▪the standard parallels are user defined, so each map can be optimized for a specific region
-is a conformal map so shape is preserved, but NOT equal-area

42
Q

if you want to use a map for navigation, you’d be best off with an ______ or _______ projection

if you are preparing a thematic display of GDP in countries around the world, you’d probably prefer an _______ or ______ projection

A

equidistant or azimuthal projection

equal-area or conformal

43
Q

compromise maps

A

these maps have distortion in everything, but the distortion is minimized so that the map appears to look how we expect the world to –these maps are typically global scale and used for display purposes

44
Q

Miller cylindrical

A

▪ a modification of the Mercator

▪ commonly used in atlases because the shape fits the standard shape of a page of paper

45
Q

Robinson Projection(compromise projection)

A

▪ minimizes visually disturbing distortions that make many world projections unattractive for general use

46
Q

▪ Winkel Tripel projection

A

▪ used by the National Geographic Society for maps because it provides an attractive balance between size and shape of features
.VERY popular but very innacurate

47
Q

Peters projection ex:

A

▪ historian Arlo Peters suggested that the Mercator projection was based on a colonial and racist attitude (the rich, northern countries are typically distorted to a greater size), and so suggested a new projection that supposedly fixed that problem
▪ this is an example of map propaganda –the use of map projection to bias the viewpoint of the observer

48
Q

Indicatrix

A

is a geometric deformation indicator that is an infinitely small circle on the surface of Earth projected as a small ellipse on a map projection plane
▪ the geometry of the circle changes during the transformation from the globe to the map, and thus can be used to demonstrate the type and degree of distortion on the map
-all the same size on the globe

Y3 T2 Geography 322 (16 decks)

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