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BASIC SPATIAL ANALYSIS TOOLS IN A GIS
database queries basic statistics buffering overlay reclassification
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GIS ANALYSIS TOOLS
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GIS ANALYSIS TOOLS Database tools: query and summarize (similar to
spreadsheet or database program
contains spatial component
Grid-based: buffering, overlay and map calculator tools
Image processing and terrain analysis: based on moving window that create new maps from
patterns on the original
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QUERIESAsk questions about GIS databases:
Where are the older stands?
Which roads are paved?
Which trails are authorized?
Which water sources are within a certain distance of a road?
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QUERIESWhere are the thinnable stands?
Age 30 and Age 40 Age 30 and Age 40 and MBF 30
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QUERIESStructured Query Language (SQL)
uses standard operators
e.g. = > < + - *
“and” “or” “not”
standard order of operations
add/subtract before multiply/divide
use parentheses to “isolate” terms
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QUERIESExample:
select stands greater than 30 acres with grass understories and a mean quadratic diameter less than 20 inches.
query for above:
(area > 30) and (understory = “grass”) and (QMD < 20)
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QUERIES
#Y#Y#Y
#Y #Y
Which water sources are within a certain distance of a road?
we need more information.
perhaps a new database layer.
“buffering” may help answer this question
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BASIC STATISTICS statistics can help determine meaning within the
data
simple, sum, count, mean, maximum, range, variance and standard deviation
calculates statistics for a combination of fields, for example:
by combining the ‘State’ name field & ‘Population’ fields, we can calculate the average state population
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BUFFERING
defining closed areas (polygons) within a certain distance of selected landscape features:
to identify areas surrounding geographic features
identify / select features that then fall within / outside the boundary of the buffer
provide summary measures of proximity
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BUFFERING
you can buffer points, lines and polygons
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BUFFERING
What do the riparian buffer zones look like?
How far around an owl nest location is 70 acres?
What do the visually sensitive areas around trails encompass?
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BUFFERING
problems may occur when buffering very convoluted lines or areas; or for large datasets
may have to increase the virtual memory of your system
or break the job up into a number of smaller pieces
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BUFFERINGSite selection determine location of new well – make sure it does
not fall within 10km of chemical factories find all stream segments within 300 feet of a
proposed logging area
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BUFFERING
Environmental pollution zone of noise pollution around major roads buffers around contaminated land to prioritise sites
(according to land use, water courses & ground water protection zones)
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BUFFERING
Resource management / Planning
service zones (e.g. 2,000 m around recycling centres)
create protection zones around features (e.g. nature reserves)
e.g. Bus routes
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BUFFERING
Epidemiology disease clusters around certain features (e.g. asthma
surrounding incinerators)
Crime to examine if car crime
is more prominent in certain areas (e.g. close to major roads, street corners, car parks)
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OVERLAY processes involving two (or more) layers
merging is a simple overlay process that combines two or more layers into one. It leaves overlapping regions and does not create new attributed polygons where there is overlap.
three overlay processes are considered here:• Union• Intersect• Identity
in contrast to a simple merge, each of these operations will produce a new layer with unique combinations of the input database polygons.
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OVERLAY
Laying one GIS database on another to produce a combination of the two.
Union:
determining the combination of two GIS databases.
resulting GIS database will extend as far as both input
GIS databases extend
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OVERLAY
Union: What is the combination of the stands and the fire area?
Input GIS database #1
Input GIS database #2
Output GIS database
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OVERLAY
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OVERLAY
Laying one GIS database on another to produce a combination of the two
Intersect:
finding the overlapping areas between two GIS databases
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OVERLAY
Intersect: Where do the stands and the fire area overlap?
Input GIS database #1
Input GIS database #2
Output GIS database
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OVERLAY
Laying one GIS database on another to produce a combination of the two.
Identity:
determining how one GIS database can be modified by the position of features in another.
limited to the spatial extent of the first GIS database.
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OVERLAY
Identity: Where does the fire occur in the stands database?
Input GIS database #1
Input GIS database #2
Output GIS database
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BOOLEAN OPERATORS Definitions
– to retrieve geographical data
– essential part of most GIS projects Usages
– to retrieve geographical data
– to check the quality of data and the results obtained (i.e. hotels in the sea after digitising or data conversion)
Boolean operators
– A AND B, A OR B, A NOT B, A XOR B, (A AND B) OR C, A AND (B OR C)
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BOOLEAN OPERATORS 1 = ‘true’ 0 = ‘false’
A B NOT A A AND B A OR B A XOR B
1 1 0 1 1 0
1 0 0 0 1 1
0 1 1 0 1 1
0 0 1 0 0 0
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BOOLEAN OPERATORS Venn diagrams
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BOOLEAN OPERATORS
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Point in Polygon
overlay point objects on areas, compute "is contained in" relationship
points a,b,c...n, are contained within polygon x
result is a new attribute for each point in the database
OVERLAY TYPES - VECTOR
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Line on Polygon
overlay line objects on area objects
compute "is contained in" relationship
lines are broken at each area object boundary
containing area is new attribute of each output line
OVERLAY TYPES - VECTOR
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Polygon on Polygon
overlay two layers of area objects
boundaries are broken at each intersection
number of output areas likely to be greater than the total number of input areas
after overlay we can recreate either of the input layers by dissolving and merging based on the attributes contributed by the input layer
OVERLAY TYPES - VECTOR
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OVERLAY TYPES - VECTOR
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very fast and easy compared to vector overlay
extent of calculations is much less
cell-by-cell basic
new cells are assigned attributes composed from original cells
condition: both layers have identical geometry
quantitative or qualitative overlay
less flexibility with attributes
OVERLAY TYPES - RASTER
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OVERLAY TYPES - RASTER raster maps treated
as arrays of numbers to be added, subtracted, etc.
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High slope (red)+
Private land (blue)
=
Potential areas for a ski resort (brown)
OVERLAY TYPES - RASTER
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OVERLAY TYPES - RASTERMap Algebra operators arithmetic operators: +, -, *, /, ^,
– grid2 = grid0 + grid1
logical operators, =, >, <, >=, <=, <>, etc.– grid2 = grid0 > grid1 (grid2 becomes 1 where this is true, 0
where false)
mathematical functions (trigonometric, logorithms, etc.)– grid2 = sin(grid1)
best raster systems allow multiple input grids– grid5 = grid1 * ( grid2 + grid3 - grid4 )– Saves calculating and storing intermediate grids
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input is result of classification
grouping of attributes according to limits with no change in geometry
results usually in a lower number of classes
aim:
to remove detail to emphasize spatial patterns
visualize new pattern and connections
transformation from one classification system to another (e.g. soil types to agricultural land use suitability)
RECLASSIFICATION
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RECLASSIFICATION
Household Income0 – 50005000 – 10,00010,000 – 20,00020,000 – 40,00040,000 – 60,00050,000 – 75,000> 75,000
Low Income Group
Middle Income Group
High Income Group
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RECLASSIFICATION results usually in a lower number of classes
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movement or distribution of resources across a connected network or arcs.
routing optimum path between two locations
allocating maximize capacity at a facility
e.g. assign streets to fire stations address Matching
locate street address along an arc based on address
NETWORK ANALYSIS
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three dimensional analysis (x,y,z)
lattice or TIN (Triangulated Irregular Network)
viewshed, profile, volume, slope, aspect
not always based on elevation
e.g. pollution, climate data, water table, etc…
SURFACE ANALYSIS