GEOG 222 Flashcards
1
Q
GIS
A
geographic information system
2
Q
spatial dependence
A
many events depend on their location
-eg. plant growth - slope? sun? nutrients?..
3
Q
what is a map
A
a form of communication
4
Q
what is a geographic information system
A
a system for -capturing -storing -checking -integrating -manipulating -analysing -displaying data which are spatially reference to Earth
5
Q
spatial data
A
- collection of measurements taken at specific locations
- mappable
6
Q
why are maps distorted
A
making a 3D object 2D
7
Q
how do we unroll the globe to make it flat
A
projections
8
Q
how do we manage spatial locations
A
coordinates
9
Q
Early Earth models
A
- oyster (Babylonians)
- rectangular box
- circular disk
- cylindrical column
- spherical ball
- very round pear
- flat earth
10
Q
Earth’s shape
A
oblate spheroid
- squashed 1/298th
- equatorial bulge ca. 42km
11
Q
georeferencing requires
A
projections
coordinates
scale
12
Q
Earth’s surface
A
Ellipsoid surface
Topographic surface
Geoid surface
13
Q
ellipsoid surface
A
- mathematical expectation of the surface based on location
- no single ellipsoid for entire Earth
14
Q
Geoid surface
A
mean sea level in the absence of winds, currents, tides
-based on gravitation
15
Q
geodetic datum
A
-link between reference ellipsoid and geoid
16
Q
how to start geodetic datum
A
- start w/ pt of known location, found using astronomical technique or GPS
- expressed in terms of lat/long
- All coordinates on Earth are referenced to a horizontal datum
17
Q
geodetic datum examples
A
NAD 27
NAD 83
18
Q
NAD 27
A
- North American Datum of 1927
- based on centre of US
- Clark Ellipsoid
- semi major 6,378,206.4m
- semi minor 6,356,583.8m
- flattening 1:294.97869
19
Q
semi major
A
horizontal axis
20
Q
semimajor axis
A
- longest diameter
- line segment that runs through the center and both foci
- ends at the widest points of the perimeter
21
Q
globe
A
- doesnt need projection
- preserves: directions, angles, distances, angles, areas
22
Q
globe disadvantages
A
- very small scale, little detail
- costly to reproduce/ update
- difficult to carry, store
23
Q
map projection
A
transformation of 3D surface to 2D
- direct geometric projection OR
- mathmatically derived transformation
- easier, cheaper, more detailed
24
Q
map projection problem
A
distortion!
25
map projections centred at 39N and 96W
- Mercator
- Lambert Conformal Conic
- Un-projected latitude and longitude
26
39N and 96W
middle of US
| Kansas
27
Characteristics of map projections
1. Class
2. Case
3. Aspect
28
Map Projections, Class
developable surface
- cylinder
- conde
- plane
29
cylindrical projection
- distors high latitudes
- longitudes are straight, parallel, equal spaced
- latitudes are straight but not equal as top of earth is 'unwrapped'
30
example of cylindrical projection distortion
Greenland looks nearly the same size as Africa
31
conic projection
- wrap a cone of paper around the Earth
- longitudes: straight lines, diverging
- latitudes: circular, around poles
32
Planar projection
long. - straight, equally spaced, radiate from centre
lat. - centric circles, equal spacing
- 'bicycle wheel'
33
Map projection characteristics, case
where and how DS intersects with RG
34
Map projection cases
tangent- DS touches RG along one line or point
| secant- through 2 points on either side, DS passes through RG
35
DS
developable surface
36
RG
reference globe
37
Map projection characteristics, aspect
- position of the projection centre w.r.t. RG
| - defines latitude of origin
38
map projection aspects
equatorial
polar
oblique
39
oblique aspect
between pole and equator
40
components that we try to preserve from distortion
- angles
- area
- distance
- direction
41
used for molar maps
planar projection
42
to preserve shapes
angles
43
Mercator
- preserves angles/ shapes
- wrong for area
- conformal
44
conformal
lat and long intersect at 90º
45
Albers equivelant conic
developer: Albers
preserves: area (equivalent)
projection: conic
46
Antarctica in Mercator
HUGE
way too big
shows that area not preserved
47
Antartica in Albers
long thing line across bottom
obviously wrong shape
preserves area
48
the "Unprojected" projection
- assumes 360º at all lats.
- y axis = lat
- x axis = longitude
- not conformal, not equal area
- nothing fully preserved
49
unprojected projection uses
-used more than should be, NASA for ex.
50
other names for the 'unprojected'
Plate Carrée
| Equirectangular
51
why use equrectangular projection
- simple to construct
- simple calculations
- high lats. are less distorted
- highest distortion away from from central parallel
52
The Fuller Projection
Dymaxion
- attempts to solve all 4 (area, angle, distance, direction)
- icosahedron (20-sided)
53
Dymaxxion =
DYnamic MAXimum tensION
54
Fuller projection advantages
- can see how all continents are connected
- minimal distortion
- easier to work with
55
Tissot's Indicatrix
- measures and illustrates distortions in projections
| - representation of the scale factor
56
Cartesian Coordinates
- based on user-defined origin
- recorded as X, Y
- suggests 1ºX = 1ºY
57
Graticules
network of lines representing the Earth's parallels of latitude and meridians of longitude
58
longitude
λ
| used in East - West measurements
59
UTM
Universal Transverse Mercator
- cylindrical, conformal, transverse mercator
- internationally standard coordinate system
60
transverse mercator
cylinder touches Earth along a meridian of longitude not the equator
61
UTM Zones
- 60 zones
- 6º long
- each w/ a Central Meridian
62
latitude
Φ
| North - South measurement
63
UTM Zone 1
180 -174ºW
| -CM: 177ºW
64
UTM coordinates
In NH: define equator as 0mN
- CM: false Easting of 500,000 mE
- Easting and Northings in m's
65
UTM georeference
zone, 6-digit Easting, 7-digit northing
| ex. 14, 468324mE, 5362789mE
66
FSA
-forward sortation area
-first 3 digits of postal code
First letter = province
Number = rural or urban
Third digit = more precise geographic location
67
each UTM is a
projection
68
RF
representative factor
- ratio btw distance on map and corresponding distance on ground
- 1: ground distance/map distance
69
verbal statement of RF
one centimetre corresponds to one kilometre
| -1cm DOES NOT EQUAL 1km
70
large scale
-object are relatively large
-more detail
-less generalized
1/250 is a bigger number than 1/25000000
71
location
describes where a thing is
72
attribute
provides information about the 'thing'
73
object model
= entity model
- collection of self-contained objects, relationships
- objects are described by attributes
- vector = objects
74
field models
- phenomena have spatially continuous attributes
- value is possible at a infinite number of point location
- Raster = field
75
object model example
crimes - object w/ spatial location
| attributes - type, cost, police officer
76
field model example
soil salinity - every location has a measure
-cannot measure an infinite # of points
-create zones
(also, elevation)
77
Lines, Vectors
- ordered set of points
- first and last = nodes
- may be called arcs
78
Pixel
-a square w/ length = to resolution, area = length^2
79
attributes than may be recorded during data collection
```
height
income
age
distance
size
```
80
in spatial analysis we need
what - attributes
| where - location
81
databases can be organized in different ways
= database models
82
common GIS database model
RDMS
83
database rows =
spatial objects
84
database columns
object attributes
85
Queries, operators 1
AND - space between
OR - all of the 2 circles
NOT
86
topology
- science, mathematics of relationships
| - associated w/ vector representations
87
one of most unique and powerful GIS functions
topology
88
what does topology 'do'
- polygons close
| - lines connect
89
SQL
standard query language
90
Ways to select in ArcGIS
- by attribute
- by location
- feature
91
Select feature
- by cursor or by graphic (ex. features within a circle you draw)
- crude selection method
92
Proximity search
- within a distance of a location
- select by location
- "are within a distance of the source layer feature"
93
adjacency search
- select by location
| - "share a line segment with"
94
Buffer, fixed distance
- buffer distance constant
| - all features buffered to same width
95
Buffer, distance from field
various buffer widths applied in same operation
96
Geodesic buffer
- accounts for shape of Earth (ellipsoid, geoid) in the calculations
- more accurate for large areas, greater than 1 UTM
97
Cartesian buffer
= Euclidean buffer
- distances calculated btw points on a plane
- more common
- best in relatively small areas (like one UTM zone_
98
most accurate buffer
geodesic
99
problem with geodesic buffer
more time to generate
100
geodesic line
shortest path between two points on an ellipsoid
101
spatial analysis requires
both
- attributes
- locations
102
buffer
- a zone around a map feature measured in units of distance or time
- a polygon enclosing a point, line, or polygon at a specified distance
103
geoprocessing
-generating a new layer by performing an action/transformation on another layer and then a query
104
RDMS
relational database management system
105
FID
feature identification
- unique code for every polygon
- no repeats
106
Proximity
analysis in which features (points, lines, polygons) are selected based on their distance from other features
107
parallels
- line of latitude
- parallel to equator
- a position north or south of equator
- unequal lengths
108
Convert 48º 27' 51" N into decimal degrees
51" / 60" = 0.85'
27.85' / 60 = 0.4641666666º
= 48.4642ºN
109
number of UTMs
60
110
numbering of UTM zones
```
1 = 180º W
30 = 0º
60 = 180º E
```
111
significant figures in decial degrees
- 4 decimal places if minutes and seconds are present
| - 2 decimal places if only minutes are present
112
convert 123.9858º W into degrees minutes seconds
0.9858º x 60' = 59.148'
0.148' x 60" = 8.88
= 123º 59' 9"
** no decimals on seconds
113
Meridians
- linges of longitude
| - East - West positions
114
UTM zone latitudes
80ºS - 84ºN
115
Polar regions and UTM zones?
not included in UTM zones
| -use UPS grid system
116
0º longitude
Prime Meridian
| -Greenwich England
117
UPS grid system, polar regions
Universal Polar Stereographic grid system
118
calculate which UTM zone a point is in
West of Greenwich: (180º - long. of city) / 6º
East of Greenwich: (180º + long. of city) / 6º
*** always round UP
119
UTM grid
designated by Eastings and Northings
| -on 1:50,000 map, grid is 1000m x 1000m squares
120
Eastings
- vertical lines references from zones central meridian
- referred to as 'false Eastings' b/c central meridian is arbitrarily assigned to 500,000m
- listed in a position before Northings
121
why is UTM CM arbitrarily assigned
so that an Easting of 0 does not occur
122
map scale
- ratio btw map distance and ground distance
- MD : GD
- scales never contain decimals
123
scale can be expressed in 3 ways
1. RF
2. Verbally
3. Graphically
124
Significant figures, trailing zeroes
```
-only sig. if decimal pt. specified
12 -> 2 sig fig
1200 -> 2 s.f.
12000 -> 12 s.f.
12.0 -> 3
```
125
significant figures, leading zeroes
never significant
0. 04 -> 1
0. 04000 -> 4
126
map projection used to show correct distance selected location and another
Equidistant map
| -all other points are distorted
127
Equivelant projection
- preserves area
| - alteres angles
128
Conformal
- projection preserves angles locally
| - shapes preserved in small areas
129
projection that correctly shows direction from one point to another
azimuthal
130
Mutually exclusive projections
- equivalent and conformal
| - no projection can preserve shape and area
131
ArcMap version
10.5
132
ways to view data in the data frame
- data view
| - layout view
133
developable surface
geometric shape that can be laid out into a flat surface without stretching or tearing
134
examples of cylindrical projections
Mercator
Plate Carre
Gall-Peters cylindrical equal-area projection
135
examples of conic projections
Lambert Conformal Conic
| Albers Equar Area Conic
136
When, on a Tissot's indicatrix map, would the circles not preserve the character of interest along the equator
- if secant --> no distortion will be along the standard parallel lines (perhaps 45º N and S)
- if centred somewhere else in a tangent
137
one of the biggest differences btw ArcMAP and others
you add data not open files
138
GIS stores two types of information on a map
1. geographic definitions of E surface features
| 2. attributes or qualities the features possess
139
vectors
- features defined by points, a single coordinate pair
| - points are connected into chains/arc and polygons
140
raster basic building block
-individual gird cell = pixel
141
raster cells represent
- categories (eg. land uses)
- magnitudes
- heights
- spectral values
- continuous or discrete data
142
spatial resolution of an image
- defined by the size of the pixel
| - 20m x 20m cell = 20m resolution
143
raster advantages
- simple data structure
- powerful
- better represent continuous data
- potentially paster processing
- stronger analyses capabilities
144
vector advantage
- more realistic
| - uses less computer space
145
raster limitations
- spatial inaccuracies due to limits of cell dimensions
| - can be very large
146
access attribute data
1. Identify tool
| 2. right-click on layer name and select open attribute table
147
smaller pixel size
- increase in number of columns and rows
| - increase in resolution
148
stretched pixel value
- image enhancement
| - change original values by increasing contrast to make easier to view
149
raster attribute table
- each pixel does not have own record
- pixels w/ same value grouped together
- count = number of pixels w/ same value
150
process of converting vector data to raster data
rasterization
151
shapefile
- simple, non topological
- for storing geometric location and attribute info
- features unique
- geometry = point, line, polygon
152
shape files contain how many files
3-8 w/ same name, different extension
153
main files associated with shape file
.shp
.shx
.dbf`
154
images
- raster layer
| - cells = brightness values of visible light
155
query categories (2 main)
attribute
| spatial
156
attribute query
uses records in attribute table to test conditions
| -ex. how many streets end with 'wood'
157
spatial query
-use info from 2+ different layers to determine how features are located w.r.t. each other
158
Query forms
1. what is here
| 2. where is this
159
what is here, query
use identify tool
160
where is here, query
select by attributes
161
adjacency
- common end point or border
| - performed on line or polygon layers only
162
why can't you perform adjacency search on points
1D - no way of being adjacent to anything
163
a query needs
1. field from which the selection will take place
2. operand
3. attribute value or expression
164
Operands
- arithmetic operators
| - =, >, >=
165
conjunction
- AND, OR, NOT
| - join 2+ queries
166
wildcards
LIKE
% - anything acceptable in its place (including nothing)
_ - means 1 character in its place
167
wildcard example with %
"NAME" LIKE '%view'
| to get names that end in view
168
wildcard example with _
"NAME" LIKE '_atherine'
169
SQL for not equal
less than greater than
| < >
170
can have a buffer outside or inside the feature
only polygons
171
types of buffers
1. Unweighted buffer (regular)
| 2. weighted buffer
172
unweighted buffer
-assume uniform width
173
weighted buffer
variable width buffer
174
example of use of weighted buffer
pollution buffer around roads
- width of buffer dependent on environment next to road
- wide for residential
- narrow for industrial
