GEOG 222 Flashcards
GIS
geographic information system
spatial dependence
many events depend on their location
-eg. plant growth - slope? sun? nutrients?..
what is a map
a form of communication
what is a geographic information system
a system for -capturing -storing -checking -integrating -manipulating -analysing -displaying data which are spatially reference to Earth
spatial data
- collection of measurements taken at specific locations
- mappable
why are maps distorted
making a 3D object 2D
how do we unroll the globe to make it flat
projections
how do we manage spatial locations
coordinates
Early Earth models
- oyster (Babylonians)
- rectangular box
- circular disk
- cylindrical column
- spherical ball
- very round pear
- flat earth
Earth’s shape
oblate spheroid
- squashed 1/298th
- equatorial bulge ca. 42km
georeferencing requires
projections
coordinates
scale
Earth’s surface
Ellipsoid surface
Topographic surface
Geoid surface
ellipsoid surface
- mathematical expectation of the surface based on location
- no single ellipsoid for entire Earth
Geoid surface
mean sea level in the absence of winds, currents, tides
-based on gravitation
geodetic datum
-link between reference ellipsoid and geoid
how to start geodetic datum
- 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
geodetic datum examples
NAD 27
NAD 83
NAD 27
- 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
semi major
horizontal axis
semimajor axis
- longest diameter
- line segment that runs through the center and both foci
- ends at the widest points of the perimeter
globe
- doesnt need projection
- preserves: directions, angles, distances, angles, areas
globe disadvantages
- very small scale, little detail
- costly to reproduce/ update
- difficult to carry, store
map projection
transformation of 3D surface to 2D
- direct geometric projection OR
- mathmatically derived transformation
- easier, cheaper, more detailed
map projection problem
distortion!
map projections centred at 39N and 96W
- Mercator
- Lambert Conformal Conic
- Un-projected latitude and longitude
39N and 96W
middle of US
Kansas
Characteristics of map projections
- Class
- Case
- Aspect
Map Projections, Class
developable surface
- cylinder
- conde
- plane
cylindrical projection
- distors high latitudes
- longitudes are straight, parallel, equal spaced
- latitudes are straight but not equal as top of earth is ‘unwrapped’
example of cylindrical projection distortion
Greenland looks nearly the same size as Africa
conic projection
- wrap a cone of paper around the Earth
- longitudes: straight lines, diverging
- latitudes: circular, around poles
Planar projection
long. - straight, equally spaced, radiate from centre
lat. - centric circles, equal spacing
- ‘bicycle wheel’
Map projection characteristics, case
where and how DS intersects with RG
Map projection cases
tangent- DS touches RG along one line or point
secant- through 2 points on either side, DS passes through RG
DS
developable surface
RG
reference globe
Map projection characteristics, aspect
- position of the projection centre w.r.t. RG
- defines latitude of origin
map projection aspects
equatorial
polar
oblique
oblique aspect
between pole and equator
components that we try to preserve from distortion
- angles
- area
- distance
- direction
used for molar maps
planar projection
to preserve shapes
angles
Mercator
- preserves angles/ shapes
- wrong for area
- conformal
conformal
lat and long intersect at 90º
Albers equivelant conic
developer: Albers
preserves: area (equivalent)
projection: conic
Antarctica in Mercator
HUGE
way too big
shows that area not preserved
Antartica in Albers
long thing line across bottom
obviously wrong shape
preserves area
the “Unprojected” projection
- assumes 360º at all lats.
- y axis = lat
- x axis = longitude
- not conformal, not equal area
- nothing fully preserved
unprojected projection uses
-used more than should be, NASA for ex.
other names for the ‘unprojected’
Plate Carrée
Equirectangular
why use equrectangular projection
- simple to construct
- simple calculations
- high lats. are less distorted
- highest distortion away from from central parallel
The Fuller Projection
Dymaxion
- attempts to solve all 4 (area, angle, distance, direction)
- icosahedron (20-sided)
Dymaxxion =
DYnamic MAXimum tensION
Fuller projection advantages
- can see how all continents are connected
- minimal distortion
- easier to work with
Tissot’s Indicatrix
- measures and illustrates distortions in projections
- representation of the scale factor
Cartesian Coordinates
- based on user-defined origin
- recorded as X, Y
- suggests 1ºX = 1ºY
Graticules
network of lines representing the Earth’s parallels of latitude and meridians of longitude
longitude
λ
used in East - West measurements
UTM
Universal Transverse Mercator
- cylindrical, conformal, transverse mercator
- internationally standard coordinate system
transverse mercator
cylinder touches Earth along a meridian of longitude not the equator
UTM Zones
- 60 zones
- 6º long
- each w/ a Central Meridian
latitude
Φ
North - South measurement
UTM Zone 1
180 -174ºW
-CM: 177ºW
UTM coordinates
In NH: define equator as 0mN
- CM: false Easting of 500,000 mE
- Easting and Northings in m’s
UTM georeference
zone, 6-digit Easting, 7-digit northing
ex. 14, 468324mE, 5362789mE
FSA
-forward sortation area
-first 3 digits of postal code
First letter = province
Number = rural or urban
Third digit = more precise geographic location
each UTM is a
projection
RF
representative factor
- ratio btw distance on map and corresponding distance on ground
- 1: ground distance/map distance
verbal statement of RF
one centimetre corresponds to one kilometre
-1cm DOES NOT EQUAL 1km
large scale
-object are relatively large
-more detail
-less generalized
1/250 is a bigger number than 1/25000000
location
describes where a thing is
attribute
provides information about the ‘thing’
object model
= entity model
- collection of self-contained objects, relationships
- objects are described by attributes
- vector = objects
field models
- phenomena have spatially continuous attributes
- value is possible at a infinite number of point location
- Raster = field
object model example
crimes - object w/ spatial location
attributes - type, cost, police officer
field model example
soil salinity - every location has a measure
-cannot measure an infinite # of points
-create zones
(also, elevation)
Lines, Vectors
- ordered set of points
- first and last = nodes
- may be called arcs
Pixel
-a square w/ length = to resolution, area = length^2
attributes than may be recorded during data collection
height income age distance size
in spatial analysis we need
what - attributes
where - location
databases can be organized in different ways
= database models
common GIS database model
RDMS
database rows =
spatial objects
database columns
object attributes
Queries, operators 1
AND - space between
OR - all of the 2 circles
NOT
topology
- science, mathematics of relationships
- associated w/ vector representations
one of most unique and powerful GIS functions
topology
what does topology ‘do’
- polygons close
- lines connect
SQL
standard query language
Ways to select in ArcGIS
- by attribute
- by location
- feature
Select feature
- by cursor or by graphic (ex. features within a circle you draw)
- crude selection method
Proximity search
- within a distance of a location
- select by location
- “are within a distance of the source layer feature”
adjacency search
- select by location
- “share a line segment with”
Buffer, fixed distance
- buffer distance constant
- all features buffered to same width
Buffer, distance from field
various buffer widths applied in same operation
Geodesic buffer
- accounts for shape of Earth (ellipsoid, geoid) in the calculations
- more accurate for large areas, greater than 1 UTM
Cartesian buffer
= Euclidean buffer
- distances calculated btw points on a plane
- more common
- best in relatively small areas (like one UTM zone_
most accurate buffer
geodesic
problem with geodesic buffer
more time to generate
geodesic line
shortest path between two points on an ellipsoid
spatial analysis requires
both
- attributes
- locations
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
geoprocessing
-generating a new layer by performing an action/transformation on another layer and then a query
RDMS
relational database management system
FID
feature identification
- unique code for every polygon
- no repeats
Proximity
analysis in which features (points, lines, polygons) are selected based on their distance from other features
parallels
- line of latitude
- parallel to equator
- a position north or south of equator
- unequal lengths
Convert 48º 27’ 51” N into decimal degrees
51” / 60” = 0.85’
27.85’ / 60 = 0.4641666666º
= 48.4642ºN
number of UTMs
60
numbering of UTM zones
1 = 180º W 30 = 0º 60 = 180º E
significant figures in decial degrees
- 4 decimal places if minutes and seconds are present
- 2 decimal places if only minutes are present
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
Meridians
- linges of longitude
- East - West positions
UTM zone latitudes
80ºS - 84ºN
Polar regions and UTM zones?
not included in UTM zones
-use UPS grid system
0º longitude
Prime Meridian
-Greenwich England
UPS grid system, polar regions
Universal Polar Stereographic grid system
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
UTM grid
designated by Eastings and Northings
-on 1:50,000 map, grid is 1000m x 1000m squares
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
why is UTM CM arbitrarily assigned
so that an Easting of 0 does not occur
map scale
- ratio btw map distance and ground distance
- MD : GD
- scales never contain decimals
scale can be expressed in 3 ways
- RF
- Verbally
- Graphically
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
significant figures, leading zeroes
never significant
- 04 -> 1
- 04000 -> 4
map projection used to show correct distance selected location and another
Equidistant map
-all other points are distorted
Equivelant projection
- preserves area
- alteres angles
Conformal
- projection preserves angles locally
- shapes preserved in small areas
projection that correctly shows direction from one point to another
azimuthal
Mutually exclusive projections
- equivalent and conformal
- no projection can preserve shape and area
ArcMap version
10.5
ways to view data in the data frame
- data view
- layout view
developable surface
geometric shape that can be laid out into a flat surface without stretching or tearing
examples of cylindrical projections
Mercator
Plate Carre
Gall-Peters cylindrical equal-area projection
examples of conic projections
Lambert Conformal Conic
Albers Equar Area Conic
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
one of the biggest differences btw ArcMAP and others
you add data not open files
GIS stores two types of information on a map
- geographic definitions of E surface features
2. attributes or qualities the features possess
vectors
- features defined by points, a single coordinate pair
- points are connected into chains/arc and polygons
raster basic building block
-individual gird cell = pixel
raster cells represent
- categories (eg. land uses)
- magnitudes
- heights
- spectral values
- continuous or discrete data
spatial resolution of an image
- defined by the size of the pixel
- 20m x 20m cell = 20m resolution
raster advantages
- simple data structure
- powerful
- better represent continuous data
- potentially paster processing
- stronger analyses capabilities
vector advantage
- more realistic
- uses less computer space
raster limitations
- spatial inaccuracies due to limits of cell dimensions
- can be very large
access attribute data
- Identify tool
2. right-click on layer name and select open attribute table
smaller pixel size
- increase in number of columns and rows
- increase in resolution
stretched pixel value
- image enhancement
- change original values by increasing contrast to make easier to view
raster attribute table
- each pixel does not have own record
- pixels w/ same value grouped together
- count = number of pixels w/ same value
process of converting vector data to raster data
rasterization
shapefile
- simple, non topological
- for storing geometric location and attribute info
- features unique
- geometry = point, line, polygon
shape files contain how many files
3-8 w/ same name, different extension
main files associated with shape file
.shp
.shx
.dbf`
images
- raster layer
- cells = brightness values of visible light
query categories (2 main)
attribute
spatial
attribute query
uses records in attribute table to test conditions
-ex. how many streets end with ‘wood’
spatial query
-use info from 2+ different layers to determine how features are located w.r.t. each other
Query forms
- what is here
2. where is this
what is here, query
use identify tool
where is here, query
select by attributes
adjacency
- common end point or border
- performed on line or polygon layers only
why can’t you perform adjacency search on points
1D - no way of being adjacent to anything
a query needs
- field from which the selection will take place
- operand
- attribute value or expression
Operands
- arithmetic operators
- =, >, >=
conjunction
- AND, OR, NOT
- join 2+ queries
wildcards
LIKE
% - anything acceptable in its place (including nothing)
_ - means 1 character in its place
wildcard example with %
“NAME” LIKE ‘%view’
to get names that end in view
wildcard example with _
“NAME” LIKE ‘_atherine’
SQL for not equal
less than greater than
< >
can have a buffer outside or inside the feature
only polygons
types of buffers
- Unweighted buffer (regular)
2. weighted buffer
unweighted buffer
-assume uniform width
weighted buffer
variable width buffer
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
