Nota GIS Kejiranan - week 11

8/10/2019 Nota GIS Kejiranan - week 11

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NeighbourhoodOperations

evaluate thecharacteristics ofan areasurrounding aspecific location.

e.g., identifyingproperties within500 m of a zonechangeapplicant:


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Analisis penampan (Buffers)

"neighbourhood" implies a relationship that

can be measured as a distance distance is a continuous variable

we naturally try to simplify distance: e.g.,

"inside or outside" , or "near or far"


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Buffer

a zone constructed outward from an object to

a specific distance commonly used in environmental regulation

to restrict activities too close to a natural

feature


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Setback

a zone constructed inward from an object to

a specific distance typically used to restrict building or activities

too close to the edge of a property parcel


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both buffers and setbacks imply a simple

zone: inside or outside the critical distance normally, a buffer or a setback is created as

a binary data set and used in an overlay to

mask out undesired areas for further

analyses


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Example: Salmon habitats vs. logging rights under the rules of exclusive ownership (pure capitalism) the owner of a

property has the right to extract the economic benefits of the land; a

logging company has the rights to remove any trees salmon return from the ocean to freshwater streams to spawn; their

reproduction depends on cold water temperatures and gravel streambottoms

removing the tree canopy near a stream can open the stream to directsunlight causing the water temperature to rise; vegetation removal can alsoincrease sediment flow in the streams, covering the gravel

government regulations have been enacted to restrict timber activities near

streams while permitting some economic benefit from the trees on the land buffers have been created within a certain distance around streams to

ensure shade and to provide enough undisturbed vegetation to trapsediment

the width of these buffers is strongly contested between the various parties


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Apa itu jiran?

Geometric Neighbours

e.g. Euclidean Distance: the distance from Point A to Point B is


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Jiran raster

neighbours are implicit in the grid

adjacent cells are either considered to be 4-connectedor 8-connected:


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Raster buffer creation:

measure Euclidean distances from a central cell draw buffer at selected distance

BUT! there is no

difference between a

2.0 and a 2.1 distance

neighbourhood

this effect decreases withdistance from target cell

and/or an increase in cell

resolution; buffer widths of

3 cell-widths or more

produce a reasonable

approximation


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it is easy to insert a barrier when measuring

raster distances; e.g. waterfalls on a canoemap

raster distances allow weights to be assigned

to each cell; e.g. steeper slopes will produce

faster ski runs


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Jiran vektor

by definition, topologcial neighbours are stored inthe database

geometric neighbours (i.e., distance) are harder toextract e.g., use an overlay operation to define a region of

interest neighbourhood

BUT! vector

representations

allow a search

radius or shape to

be of any size


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Vector buffer creation:

a circle is drawn around each vertex

a rectangle is drawn around each line segment

all of the circles and rectangles are aggregated to

remove duplicate areas

complex process generally hidden from the user


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neighbourhoods are most commonly square,

circular, or rectangular, but they need not beany regular shape, e.g. a country

search functions can be an equation: Select

hospitals with more than 500 beds and are

less than 5 years old

Nota GIS Kejiranan - week 11

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