Chapter 3 - Geodesy, Datum, Map Projections & Coordinate Systems Flashcards
1
Q
These define the location and shape of geographic entities
A
Spatial coordinates
2
Q
What are two things that complicate the process of defining coordinates?
A
- Earth is best understood with flat maps and Cartesian coordinates; 2. Earth is not a perfect sphere shape
3
Q
These are two ways to address the problem of defining coordinates
A
Geodesy and map projections
4
Q
This is a discipline concerned with measuring and representing the Earth
A
Geodesy
5
Q
What is geodesy needed to do accurately?
A
To locate points on a globe
6
Q
What was geodesy originally based on?
A
Land surveys
7
Q
What are land surveys combined with in modern geodesy?
A
Satellite telemetry
8
Q
Geodesy creates these two shapes for reference used for spatial positioning
A
Ellipsoid and geoid
9
Q
Humans have long speculated on this characteristic of the Earth
A
Shape
10
Q
What are three of five shapes considered for the Earth over human history?
A
Disc, box, sphere, pear, flat
11
Q
The Earth has often been seen as this shape
A
An infinite sea covered by a hemisphere of stars
12
Q
Who are four of seven philosophers key to the history of earth measurement?
A
Pythagoras, Plato, Aristotle, Eratosthenes, Posidonius, Ptolemy, Newton
13
Q
This philosopher postulated a spherical Earth, based purely on aesthetic reasoning
A
Pythagoras
14
Q
This philosopher postulated a published and widely accepted idea of a spherical planet for aesthetic reasons
A
Plato
15
Q
This philosopher posited the Earth was a sphere for geometric reasons and provided physical evidence
A
Aristotle
16
Q
For how long was Aristotle’s theory of a spherical Earth generally accepted?
A
700 years
17
Q
This philosopher used angles of shadows to measure the circumference of the Earth
A
Eratosthenes
18
Q
By what percentage was Eratosthenes off in his measurement of the Earth’s circumference?
A
1%
19
Q
This philosopher used star sightings to estimate the Earth’s size
A
Posidonius
20
Q
By what percentage was Posidonius off in his estimation of the Earth’s circumference?
A
18%
21
Q
This philosopher revised Posidonius’ estimation of the Earth’s size
A
Ptolemy
22
Q
By what percentage was Ptolemy off in his estimation of the Earth’s size?
A
28%
23
Q
Ptolemy’s estimation of the Earth’s size was used during this historical period
A
Renaissance
24
Q
This scientist posited that the Earth’s rotation created an ellipsoid
A
Newton
25
When was Newton's theory of the Earth's shape proven?
1730
26
In what century did serious efforts to measure the Earth arise?
18th century
27
What are two reasons why efforts to measure the Earth rise in the 18th century?
Rising need for accurate maps and availability of better instruments
28
For how many years were Earth radii repeatedly measured starting in the 18th century?
Over 200 years
29
What two methods were combined to measure the Earth since the 18th century?
Posidonius method and land surveys
30
18th century Earth measurements used these to approximate the true shape of the Earth
Reference ellipsoids
31
An ellipsoid is described by these two axes
Semi-minor axis and semi-major axis
32
What three things are defined on a reference ellipsoid?
Radii, poles and equator
33
What are three reasons why so many reference ellipsoids of the Earth were created?
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
34
These two types of modern technology have enabled precise measurement of the Earth
Satellites and lasers
35
What are the three current ellipsoids?
1. World Geodetic System 1972; 2. Geodetic Reference System 1980; 3. World Geodetic System 1984
36
These two types of lines form a geographic coordinate grid lain over a reference ellipsoid
Latitude and longitude
37
These coordinate lines describe positions north-south of the equator
Latitude
38
These coordinate lines describe positions east-west of a reference line
Longitude
39
What are latitude lines called?
Parallels
40
What are longitude lines called?
Meridians
41
In what year was the prime meridian set?
1884
42
What is another name for the latitude-longitude grid?
Graticule
43
This is the difference between the magnetic and geographic poles
Magnetic declination
44
This is a hypothetical surface of Earth
Geoid
45
Is a geoid smoother than a reference ellipsoid?
No
46
Is a geoid smoother than Earth's surface?
Yes
47
A geoid's shape is a result of variation in this
Earth's gravity
48
A geoid coincides with this if the oceans were extended through the continents
Mean sea level
49
For a geoid shape, this is measured for many ground points
Surface gravity
50
For a geoid shape, these are interpolated using mathematical models
Unmeasured areas
51
These tools were initially used for measuring/interpolating geoid shape
Plumb bobs
52
What are three modern tools used to measure geoid shape now?
Ground gravimeters, airplanes and satellites
53
On a planetary geoid, surface elevation is usually defined as this
Orthometric height
54
This is the difference between a geoid and an ellipsoid
Geoidal undulation
55
This explains why different ellipsoids are used in different regions
Geoidal undulation
56
These form basis for calculating the position of points on Earth
Geodetic datums
57
What is the geodetic agency for the United States?
National Geodetic Survey
58
What are the two types of geodetic datums?
Horizontal and vertical datums
59
These datums define horizontal position with lat-long or other coordinates
Horizontal datums
60
What are the two components of horizontal datums?
1. Reference ellipsoid and coordinate system; 2. Many precise ground points
61
This component of a horizontal datum comprises the theoretical model
Reference ellipsoid/coordinate system
62
This component of a horizontal datum fixes a model to the surface
Many precise ground points
63
This is a network of precise ground points
Geodetic survey
64
Historic geodetic surveys use these to precisely measure a few control points, then triangulating off of them
Stars
65
Modern geodetic surveys use these
Satellites
66
This process uses trigonometry to position points in geodetic surveys
Triangulation
67
Between what years did the Great Trigonometric Survey of India take place?
1802-1866
68
These are monumented datum points
Benchmarks
69
What are the three common geodetic datums used in the U.S.?
1. North American Datum of 1927 (NAD27); 2. North American Datum of 1983 (NAD83); 3. World Geodetic System of 1984 (WGS84)
70
Who performed the North American Datum of 1927?
U.S. Coast and Geodetic Survey
71
Which ellipsoid did the North American Datum of 1927 use as a reference?
Clark 1886 ellipsoid
72
What did the North American Datum of 1927 use as a base point?
Meades Ranch, KS
73
How many survey stations were involved in the North American Datum of 1927?
26,000
74
Who performed the North American Datum of 1983?
National Geodetic Survey
75
What did the North American Datum of 1983 use as references?
GRS80 ellipsoid and geocentric origin
76
How many survey stations were involved in the North American Datum of 1983?
250,000
77
Who performed the World Geodetic System of 1984?
Department of Defense
78
What did the World Geodetic System of 1984 use as references?
WGS84 ellipsoid and geocentric origin
79
This results in benchmarks having different lat-long with different datums
Datum shift
80
This uses math conversion to estimate datum shift
Datum transformation
81
Between what two datums have the largest datum shifts occurred?
NAD27 and newer datums
82
Are shifts with modern datums usually large?
No
83
Is transforming NAD27 to modern datums complicated?
Yes
84
Is transforming between modern datums complicated?
No
85
Do NAD83 and WGS84 have their own transformations?
Yes
86
Should GIS projects mix datums?
No
87
Should caution be used when transforming datums?
Yes
88
This type of datum is used for defining surface elevations
Vertical datums
89
Vertical datums use a network of these
Established ground points
90
Vertical datums include precise measurements of these two things
Elevation and gravity
91
Do vertical datums share many stations with horizontal datums?
Yes
92
Vertical datums used these historically
Leveling surveys
93
Where do vertical datums start and end?
Ocean to inland
94
In modern vertical datums, what are surface elevations estimated with?
Satellites
95
What are two common North American datums?
National Geodetic Vertical Datum of 1929 (NGVD29) and North American Vertical Datum of 1988 (NAVD88)
96
Leveling surveys use this to estimate height
Trigonometry
97
These are flat representations of the Earth's surface
Map projections
98
Map projections are easier to use/analyze than these representations of the Earth
Globes
99
What are three of five key properties of maps?
Scale, shape, area, distance, direction
100
Map projections are a systematic transfer of these to a flat surface
Points on datum
101
Will all map projections distort the Earth?
Yes
102
Do map projections distort all map properties?
No
103
Do map projections preserve some properties and distort others?
Yes
104
Can distortion change within a single map?
Yes
105
Where is distortion lowest on a map?
Near intersection of ellipsoid and map
106
Do all maps have a point or line where distortion is zero?
Yes
107
The shortest path on a globe is represented by this on a map
Arc
108
What are the three parameters of projections?
1. Projection surface; 2. Projection perspective; 3. Projection aspect
109
What are three common projection surfaces/shapes?
Cylinder, cone, plane
110
What are three common map projection perspectives?
Gnomonic, stereographic, orthographic
111
What are three map projection aspects?
Normal, transverse, oblique
112
What are two map projections used in GIS?
Lambert Conformal Conic and Transverse Mercator
113
This map projection uses a conical surface
Lambert Conformal Conic
114
These are the two lines of latitude that intersect the ellipsoid in the Lambert Conformal Conic map projection
Standard parallels
115
How much distortion do standard parallels have in a Lambert Conformal Conic map projection?
Zero
116
What can be done to control distortion on a Lambert Conformal Conic map projection?
Change position of parallels
117
What direction does the low distortion band run on a Lambert Conformal Conic map projection?
East-West
118
The Lambert Conformal Conic map projection is a good projection for this type of region
Wide regions
119
This map projection uses a cylindrical surface
Transverse Mercator
120
In what places does the Transverse Mercator map projection intersect the ellipsoid?
Along one tangent or two secant lines
121
Where is distortion lowest on a Transverse Mercator map projection?
Near intersection
122
In a Transverse Mercator map projection, what can be changed to control distortion?
Secant positions
123
This is the line of longitude between secants in a Transverse Mercator map projection
Central meridian
124
Which way does the low distortion band run in a Transverse Mercator map projection?
North-South
125
The Transverse Mercator map projection is a good projection for this type of region
Tall regions
126
This projection system is used by U.S. states
State Plane System
127
What are three fields that use the State Plane System?
Surveying, construction, GIS
128
The State Plane System converts this to an x-y coordinate system
Lat-long
129
In the State Plane System, does each state use its own coordinates and origin?
Yes
130
In the State Plane System, states are zonated to reduce this
Distortion
131
How many zones can a state have in the State Plane System?
1-6
132
In the State Plane System, to what maximum is distortion kept?
1 part in 10,000
133
Do all states use the same map projection type in the State Plane System?
No
134
What map projection do tall states use?
Transverse Mercator
135
What map projection do wide states use?
Lambert Conic
136
Can a state use both map projections for different zones?
Yes
137
The State Plane System was first developed for this datum
NAD27
138
This datum introduced some changes to the State Plane System
NAD83
139
This is a global position coordinate system
Universal Transverse Mercator System
140
Into how many zones does the Universal Transverse Mercator System split the globe?
60 zones
141
How wide is each global zone in the Universal Transverse Mercator System?
6 degrees
142
Between what two boundaries does the Universal Transverse Mercator System extend?
From 80 degrees South to 84 degrees North
143
How much overlap is there between zones in the Universal Transverse Mercator System?
40 km
144
In the Universal Transverse Mercator System, each zone is split into what two zones?
North and south
145
What does the Universal Transverse Mercator System use in its coordinate system?
Meters from origin
146
In the Universal Transverse Mercator System, is the cylinder ellipsoid smaller or larger than Earth's diameter?
Smaller
147
Can spatial data use different map projections when working in GIS?
No
148
Can map projections be converted?
Yes
149
GIS software uses these to transform coordinates
Math equations
150
Complex transformations can include both these types of conversions
Datum and map projection conversions
151
In converting map projections without datum conversion, map projection coordinates must be first back-converted to these
Geographic coordinates
152
Is converting map projections with different datums simple to do?
No
153
Converting map projections with datum conversion requires this step
Datum conversion step
154
This is a U.S. land parcel coordinate system
Public Land Survey System
155
The original U.S. colonies used this land parcel system
Metes and bounds
156
The metes and bounds system uses these to bind parcels
Geography and local markers
157
In what year was the Public Land Survey System established by Congress?
1785
158
What are the two basic Public Land Survey System units of area?
Township and section
159
What are the dimensions of a township in the Public Land Survey System?
6x6 mile parcel
160
Into how many sections is a township divided in the Public Land Survey System?
36
161
In the Public Land Survey System, townships are located with these two coordinates
Township and range coordinates
162
What are the dimensions of a section in the Public Land Survey System?
1x1 mile parcel
163
Into what is a section divided in the Public Land Survey System?
Quarters and small parcels
164
In the Public Land Survey System, township and range coordinates use these two types of lines
Principal meridians and baselines
