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Fundamentals of GIS > Chapter 3 - Geodesy, Datum, Map Projections & Coordinate Systems > Flashcards

Chapter 3 - Geodesy, Datum, Map Projections & Coordinate Systems Flashcards

1
Q

These define the location and shape of geographic entities

A

Spatial coordinates

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2
Q

What are two things that complicate the process of defining coordinates?

A
  1. Earth is best understood with flat maps and Cartesian coordinates; 2. Earth is not a perfect sphere shape
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3
Q

These are two ways to address the problem of defining coordinates

A

Geodesy and map projections

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4
Q

This is a discipline concerned with measuring and representing the Earth

A

Geodesy

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5
Q

What is geodesy needed to do accurately?

A

To locate points on a globe

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6
Q

What was geodesy originally based on?

A

Land surveys

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7
Q

What are land surveys combined with in modern geodesy?

A

Satellite telemetry

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8
Q

Geodesy creates these two shapes for reference used for spatial positioning

A

Ellipsoid and geoid

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9
Q

Humans have long speculated on this characteristic of the Earth

A

Shape

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10
Q

What are three of five shapes considered for the Earth over human history?

A

Disc, box, sphere, pear, flat

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11
Q

The Earth has often been seen as this shape

A

An infinite sea covered by a hemisphere of stars

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12
Q

Who are four of seven philosophers key to the history of earth measurement?

A

Pythagoras, Plato, Aristotle, Eratosthenes, Posidonius, Ptolemy, Newton

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13
Q

This philosopher postulated a spherical Earth, based purely on aesthetic reasoning

A

Pythagoras

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14
Q

This philosopher postulated a published and widely accepted idea of a spherical planet for aesthetic reasons

A

Plato

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15
Q

This philosopher posited the Earth was a sphere for geometric reasons and provided physical evidence

A

Aristotle

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16
Q

For how long was Aristotle’s theory of a spherical Earth generally accepted?

A

700 years

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17
Q

This philosopher used angles of shadows to measure the circumference of the Earth

A

Eratosthenes

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18
Q

By what percentage was Eratosthenes off in his measurement of the Earth’s circumference?

A

1%

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19
Q

This philosopher used star sightings to estimate the Earth’s size

A

Posidonius

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20
Q

By what percentage was Posidonius off in his estimation of the Earth’s circumference?

A

18%

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21
Q

This philosopher revised Posidonius’ estimation of the Earth’s size

A

Ptolemy

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22
Q

By what percentage was Ptolemy off in his estimation of the Earth’s size?

A

28%

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23
Q

Ptolemy’s estimation of the Earth’s size was used during this historical period

A

Renaissance

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24
Q

This scientist posited that the Earth’s rotation created an ellipsoid

A

Newton

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25
Q

When was Newton’s theory of the Earth’s shape proven?

A

1730

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26
Q

In what century did serious efforts to measure the Earth arise?

A

18th century

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27
Q

What are two reasons why efforts to measure the Earth rise in the 18th century?

A

Rising need for accurate maps and availability of better instruments

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28
Q

For how many years were Earth radii repeatedly measured starting in the 18th century?

A

Over 200 years

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29
Q

What two methods were combined to measure the Earth since the 18th century?

A

Posidonius method and land surveys

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30
Q

18th century Earth measurements used these to approximate the true shape of the Earth

A

Reference ellipsoids

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31
Q

An ellipsoid is described by these two axes

A

Semi-minor axis and semi-major axis

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32
Q

What three things are defined on a reference ellipsoid?

A

Radii, poles and equator

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33
Q

What are three reasons why so many reference ellipsoids of the Earth were created?

A
  1. Surveys needed points 30 miles apart; 2. Different methods were used between regions with different access to computers; 3. Earth is not a perfect ellipsoid, so an average of many is needed
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34
Q

These two types of modern technology have enabled precise measurement of the Earth

A

Satellites and lasers

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35
Q

What are the three current ellipsoids?

A
  1. World Geodetic System 1972; 2. Geodetic Reference System 1980; 3. World Geodetic System 1984
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36
Q

These two types of lines form a geographic coordinate grid lain over a reference ellipsoid

A

Latitude and longitude

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37
Q

These coordinate lines describe positions north-south of the equator

A

Latitude

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38
Q

These coordinate lines describe positions east-west of a reference line

A

Longitude

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39
Q

What are latitude lines called?

A

Parallels

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40
Q

What are longitude lines called?

A

Meridians

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41
Q

In what year was the prime meridian set?

A

1884

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42
Q

What is another name for the latitude-longitude grid?

A

Graticule

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43
Q

This is the difference between the magnetic and geographic poles

A

Magnetic declination

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44
Q

This is a hypothetical surface of Earth

A

Geoid

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45
Q

Is a geoid smoother than a reference ellipsoid?

A

No

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46
Q

Is a geoid smoother than Earth’s surface?

A

Yes

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47
Q

A geoid’s shape is a result of variation in this

A

Earth’s gravity

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48
Q

A geoid coincides with this if the oceans were extended through the continents

A

Mean sea level

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49
Q

For a geoid shape, this is measured for many ground points

A

Surface gravity

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50
Q

For a geoid shape, these are interpolated using mathematical models

A

Unmeasured areas

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51
Q

These tools were initially used for measuring/interpolating geoid shape

A

Plumb bobs

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52
Q

What are three modern tools used to measure geoid shape now?

A

Ground gravimeters, airplanes and satellites

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53
Q

On a planetary geoid, surface elevation is usually defined as this

A

Orthometric height

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54
Q

This is the difference between a geoid and an ellipsoid

A

Geoidal undulation

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55
Q

This explains why different ellipsoids are used in different regions

A

Geoidal undulation

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56
Q

These form basis for calculating the position of points on Earth

A

Geodetic datums

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57
Q

What is the geodetic agency for the United States?

A

National Geodetic Survey

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58
Q

What are the two types of geodetic datums?

A

Horizontal and vertical datums

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59
Q

These datums define horizontal position with lat-long or other coordinates

A

Horizontal datums

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60
Q

What are the two components of horizontal datums?

A
  1. Reference ellipsoid and coordinate system; 2. Many precise ground points
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61
Q

This component of a horizontal datum comprises the theoretical model

A

Reference ellipsoid/coordinate system

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62
Q

This component of a horizontal datum fixes a model to the surface

A

Many precise ground points

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63
Q

This is a network of precise ground points

A

Geodetic survey

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64
Q

Historic geodetic surveys use these to precisely measure a few control points, then triangulating off of them

A

Stars

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65
Q

Modern geodetic surveys use these

A

Satellites

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66
Q

This process uses trigonometry to position points in geodetic surveys

A

Triangulation

67
Q

Between what years did the Great Trigonometric Survey of India take place?

A

1802-1866

68
Q

These are monumented datum points

A

Benchmarks

69
Q

What are the three common geodetic datums used in the U.S.?

A
  1. North American Datum of 1927 (NAD27); 2. North American Datum of 1983 (NAD83); 3. World Geodetic System of 1984 (WGS84)
70
Q

Who performed the North American Datum of 1927?

A

U.S. Coast and Geodetic Survey

71
Q

Which ellipsoid did the North American Datum of 1927 use as a reference?

A

Clark 1886 ellipsoid

72
Q

What did the North American Datum of 1927 use as a base point?

A

Meades Ranch, KS

73
Q

How many survey stations were involved in the North American Datum of 1927?

A

26,000

74
Q

Who performed the North American Datum of 1983?

A

National Geodetic Survey

75
Q

What did the North American Datum of 1983 use as references?

A

GRS80 ellipsoid and geocentric origin

76
Q

How many survey stations were involved in the North American Datum of 1983?

A

250,000

77
Q

Who performed the World Geodetic System of 1984?

A

Department of Defense

78
Q

What did the World Geodetic System of 1984 use as references?

A

WGS84 ellipsoid and geocentric origin

79
Q

This results in benchmarks having different lat-long with different datums

A

Datum shift

80
Q

This uses math conversion to estimate datum shift

A

Datum transformation

81
Q

Between what two datums have the largest datum shifts occurred?

A

NAD27 and newer datums

82
Q

Are shifts with modern datums usually large?

A

No

83
Q

Is transforming NAD27 to modern datums complicated?

A

Yes

84
Q

Is transforming between modern datums complicated?

A

No

85
Q

Do NAD83 and WGS84 have their own transformations?

A

Yes

86
Q

Should GIS projects mix datums?

A

No

87
Q

Should caution be used when transforming datums?

A

Yes

88
Q

This type of datum is used for defining surface elevations

A

Vertical datums

89
Q

Vertical datums use a network of these

A

Established ground points

90
Q

Vertical datums include precise measurements of these two things

A

Elevation and gravity

91
Q

Do vertical datums share many stations with horizontal datums?

A

Yes

92
Q

Vertical datums used these historically

A

Leveling surveys

93
Q

Where do vertical datums start and end?

A

Ocean to inland

94
Q

In modern vertical datums, what are surface elevations estimated with?

A

Satellites

95
Q

What are two common North American datums?

A

National Geodetic Vertical Datum of 1929 (NGVD29) and North American Vertical Datum of 1988 (NAVD88)

96
Q

Leveling surveys use this to estimate height

A

Trigonometry

97
Q

These are flat representations of the Earth’s surface

A

Map projections

98
Q

Map projections are easier to use/analyze than these representations of the Earth

A

Globes

99
Q

What are three of five key properties of maps?

A

Scale, shape, area, distance, direction

100
Q

Map projections are a systematic transfer of these to a flat surface

A

Points on datum

101
Q

Will all map projections distort the Earth?

A

Yes

102
Q

Do map projections distort all map properties?

A

No

103
Q

Do map projections preserve some properties and distort others?

A

Yes

104
Q

Can distortion change within a single map?

A

Yes

105
Q

Where is distortion lowest on a map?

A

Near intersection of ellipsoid and map

106
Q

Do all maps have a point or line where distortion is zero?

A

Yes

107
Q

The shortest path on a globe is represented by this on a map

A

Arc

108
Q

What are the three parameters of projections?

A
  1. Projection surface; 2. Projection perspective; 3. Projection aspect
109
Q

What are three common projection surfaces/shapes?

A

Cylinder, cone, plane

110
Q

What are three common map projection perspectives?

A

Gnomonic, stereographic, orthographic

111
Q

What are three map projection aspects?

A

Normal, transverse, oblique

112
Q

What are two map projections used in GIS?

A

Lambert Conformal Conic and Transverse Mercator

113
Q

This map projection uses a conical surface

A

Lambert Conformal Conic

114
Q

These are the two lines of latitude that intersect the ellipsoid in the Lambert Conformal Conic map projection

A

Standard parallels

115
Q

How much distortion do standard parallels have in a Lambert Conformal Conic map projection?

A

Zero

116
Q

What can be done to control distortion on a Lambert Conformal Conic map projection?

A

Change position of parallels

117
Q

What direction does the low distortion band run on a Lambert Conformal Conic map projection?

A

East-West

118
Q

The Lambert Conformal Conic map projection is a good projection for this type of region

A

Wide regions

119
Q

This map projection uses a cylindrical surface

A

Transverse Mercator

120
Q

In what places does the Transverse Mercator map projection intersect the ellipsoid?

A

Along one tangent or two secant lines

121
Q

Where is distortion lowest on a Transverse Mercator map projection?

A

Near intersection

122
Q

In a Transverse Mercator map projection, what can be changed to control distortion?

A

Secant positions

123
Q

This is the line of longitude between secants in a Transverse Mercator map projection

A

Central meridian

124
Q

Which way does the low distortion band run in a Transverse Mercator map projection?

A

North-South

125
Q

The Transverse Mercator map projection is a good projection for this type of region

A

Tall regions

126
Q

This projection system is used by U.S. states

A

State Plane System

127
Q

What are three fields that use the State Plane System?

A

Surveying, construction, GIS

128
Q

The State Plane System converts this to an x-y coordinate system

A

Lat-long

129
Q

In the State Plane System, does each state use its own coordinates and origin?

A

Yes

130
Q

In the State Plane System, states are zonated to reduce this

A

Distortion

131
Q

How many zones can a state have in the State Plane System?

A

1-6

132
Q

In the State Plane System, to what maximum is distortion kept?

A

1 part in 10,000

133
Q

Do all states use the same map projection type in the State Plane System?

A

No

134
Q

What map projection do tall states use?

A

Transverse Mercator

135
Q

What map projection do wide states use?

A

Lambert Conic

136
Q

Can a state use both map projections for different zones?

A

Yes

137
Q

The State Plane System was first developed for this datum

A

NAD27

138
Q

This datum introduced some changes to the State Plane System

A

NAD83

139
Q

This is a global position coordinate system

A

Universal Transverse Mercator System

140
Q

Into how many zones does the Universal Transverse Mercator System split the globe?

A

60 zones

141
Q

How wide is each global zone in the Universal Transverse Mercator System?

A

6 degrees

142
Q

Between what two boundaries does the Universal Transverse Mercator System extend?

A

From 80 degrees South to 84 degrees North

143
Q

How much overlap is there between zones in the Universal Transverse Mercator System?

A

40 km

144
Q

In the Universal Transverse Mercator System, each zone is split into what two zones?

A

North and south

145
Q

What does the Universal Transverse Mercator System use in its coordinate system?

A

Meters from origin

146
Q

In the Universal Transverse Mercator System, is the cylinder ellipsoid smaller or larger than Earth’s diameter?

A

Smaller

147
Q

Can spatial data use different map projections when working in GIS?

A

No

148
Q

Can map projections be converted?

A

Yes

149
Q

GIS software uses these to transform coordinates

A

Math equations

150
Q

Complex transformations can include both these types of conversions

A

Datum and map projection conversions

151
Q

In converting map projections without datum conversion, map projection coordinates must be first back-converted to these

A

Geographic coordinates

152
Q

Is converting map projections with different datums simple to do?

A

No

153
Q

Converting map projections with datum conversion requires this step

A

Datum conversion step

154
Q

This is a U.S. land parcel coordinate system

A

Public Land Survey System

155
Q

The original U.S. colonies used this land parcel system

A

Metes and bounds

156
Q

The metes and bounds system uses these to bind parcels

A

Geography and local markers

157
Q

In what year was the Public Land Survey System established by Congress?

A

1785

158
Q

What are the two basic Public Land Survey System units of area?

A

Township and section

159
Q

What are the dimensions of a township in the Public Land Survey System?

A

6x6 mile parcel

160
Q

Into how many sections is a township divided in the Public Land Survey System?

A

36

161
Q

In the Public Land Survey System, townships are located with these two coordinates

A

Township and range coordinates

162
Q

What are the dimensions of a section in the Public Land Survey System?

A

1x1 mile parcel

163
Q

Into what is a section divided in the Public Land Survey System?

A

Quarters and small parcels

164
Q

In the Public Land Survey System, township and range coordinates use these two types of lines

A

Principal meridians and baselines

Fundamentals of GIS (13 decks)

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