BASIC SPATIAL ANALYSIS
TOOLS IN A GIS
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database queries
basic statistics
buffering
overlay
reclassification
GIS ANALYSIS TOOLS
GIS ANALYSIS TOOLS
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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
QUERIES
Ask 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?
QUERIES
Where are the thinnable stands?
Age  30 and Age  40
Age  30 and Age  40 and MBF  30
QUERIES
Structured Query Language (SQL)


uses standard operators

e.g. = > < + - *
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“and” “or” “not”
standard order of operations

add/subtract before multiply/divide

use parentheses to “isolate” terms
QUERIES
Example:

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)
QUERIES
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
Y
#
Y
#
Y
#
Y
#
Y
#
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
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
BUFFERING

you can buffer points, lines and polygons
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?
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
BUFFERING
Site 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
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)
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
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)
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.
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
OVERLAY
Union: What is the combination of the stands and
the fire area?
Input GIS
database #1
Input GIS
database #2
Output GIS
database
OVERLAY
OVERLAY
Laying one GIS database on another to produce a
combination of the two
Intersect:

finding the overlapping areas between two GIS
databases
OVERLAY
Intersect: Where do the stands and the fire area overlap?
Input GIS
database #1
Input GIS
database #2
Output GIS
database
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.
OVERLAY
Identity: Where does the fire occur in the stands
database?
Input GIS
database #1
Input GIS
database #2
Output GIS
database
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)
BOOLEAN OPERATORS

1 = ‘true’ 0 = ‘false’
A
B
1
1
0
0
1
0
1
0
NOT A
0
0
1
1
A AND B
1
0
0
0
A OR B A XOR B
1
1
1
0
0
1
1
0
BOOLEAN OPERATORS

Venn diagrams
BOOLEAN OPERATORS
OVERLAY TYPES - VECTOR
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
Line on Polygon

overlay line objects on area objects
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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
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
OVERLAY TYPES - RASTER
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very fast and easy compared to vector overlay



extent of calculations is much less
cell-by-cell basic
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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

raster maps treated
as arrays of numbers
to be added,
subtracted, etc.
OVERLAY TYPES - RASTER
High slope (red)
+
Private land (blue)
=
Potential areas for
a ski resort (brown)
OVERLAY TYPES - RASTER
Map 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
RECLASSIFICATION

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
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visualize new pattern and connections

transformation from one classification system to
another (e.g. soil types to agricultural land use
suitability)
RECLASSIFICATION
Household Income
0 – 5000
5000 – 10,000
10,000 – 20,000
20,000 – 40,000
40,000 – 60,000
50,000 – 75,000
> 75,000
Low Income Group
Middle Income Group
High Income Group
RECLASSIFICATION

results usually in a lower number of classes
NETWORK ANALYSIS

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
SURFACE ANALYSIS
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three dimensional analysis (x,y,z)
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lattice or TIN (Triangulated Irregular Network)
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viewshed, profile, volume, slope, aspect
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not always based on elevation
e.g. pollution, climate data, water table, etc…