GEOG 222 II Flashcards
Intersection =
only location in both remain
-AND
Union =
locations in either remain
-OR
cookie cutter tool
clip
like the opposite of the clip tool, what is left over
erase
things to watch out for with intersection and overlay
common boundaries
spurious polygons
mixing up identify and intersect
common boundaries
- may be able to see that the line looks thicker
- zoomed in there may be a new polygon from lines crossing, not quite lining up
new polygon formed from common boundaries
spurious polygon
- not there in real life
- artifact
intersect vs identify
- both calculate geometric intersection of input layers
- intersect = AND - only in common features, based on input layer, order doesn’t matter
- identity = all features of first layer + those that overlap w/ identity layer, order matters
raster
- space divided into small units
- space is tessellated
tessellation
process to cover a surface through the repeated use of a single shape
Raster shape
- any reasonable geometric shape that can be connected to create a continuous surface
- squares, triangles, hexagons
- not circles - dont interlock
best raster shape
- lattice, grid, square, rectangle
- interlock, end at edge, fit screens
- easy to deal with mathematically
- efficient to store
Information location, raster
- not explicit like coordinates
- recorded by cell location i.e. row 1, col 1
continuous raster
- infinite values
- each cell has one value
Raster issues
- grid cell size
- data storage
- only one attribute per layer
why use raster
- data storage
- efficiency and processing speed
types of raster encoding
- row by row, uncompressed
- run-length encoding
- boustrophedon
discrete raster
- limited, non-continuous numbers
- classes, eg. soil class
- pixels w/ same value = same class
- similar to polygons, eg. a group of 0’s is a water body
boustrophedon
=how oxen ploughs the field
- right across bottom row
- left across second last row
- right …
row by row encoding
- start at bottom left corner
- right on last row
- right on second last row
Raster issues, multiple attributes
- stack grids
- raster calculator
raster calculator
- operators (mathematical, boolean)
- functions
- queries
Raster calculator, mathematical operators
-arithmetic: *, /, -, +
[raster1] + [raster2]
Raster calculator, boolean operators
-AND, OR, NOT
[raster1] = 1 AND [raster2] = 4
-binary result
GPS segments
- space (24 satellites, redundancy)
- user segment (receivers)
- control segment (ground stations)
control segment
- major stations check altitude, position, speed, health of satellites
- ‘see’ 11 at a time
- checked twice a day
measuring distance with GPS
-distance = time needed for radio signal transmitted from space to user
= travel t x speed of light
satellite clock features
- 12 hours to orbit earth
- 4 atomic clocks aboard each satellite
- 1 billionth of a second precision
- radio antenna sends signal to E at speed of light
satellite distance
10’s of thousands of kms
Trilateration
number of satellites and data you can get 1= sphere 2 = circle 3 = points, intersect 4 = height, elevation
ground distance =
map distance x representative factor
why use network analysis
- control mobility and flow in discrete spaces
- movement of goods, services, information
what is a network
- set of line segments connected at nodes
- form paths and/or loops
Network links
-line segment connected to at least one other link
Network nodes
- junction of links
- end points of links
network valency
-number of links at each node
Problems with routing
- shortest path
- traveling vendor
- vehicle routing problem
optimal route types
- shortest path
- traveling vendor
shortest path
- find shortest path from origin through set of destinations
- user defined order
traveling vendor
- shortest tour from origin
- through destinations in any order
- back to origin
how shortest path works
= minimum cumulative impedance (opposition) between nodes
- build tree-like structure outward from source
- algorithm finds path of lowest cost
shortest path complexity based on number of nodes
-number of paths = n^3
Traveling vendor problem details
- most efficient order of stops
- solved heuristically
heuristics
- algorithms designed to work quickly and come close to best answer w/o guaranteeing best answer
- logical, optimal
traveling vendor problem complexity
(n-1)!/2
Heuristic method
- start w/ feasible solution
- shuffle nodes
- recalculate
- repeat until satisfied solution not improving
Vehicle routing problem
- variation of TVP
- given a fleet of vehicles and customers schedule routes and visits to minimize travel time
Network example, firestations
- Closest facility: firestations
- Incidents: house on fire
- Barriers: one-way streets, construction, etc.
- Routes
Supply and demand
location/allocation
- locate service
- allocate demand
location/allocation goals
- minimize travel
- maximize profit
Service area
- region w/i certain travelling time/distance
- polygons
- ex. pizza delivery area