BASIC SPATIAL ANALYSIS TOOLS IN A GIS

database queries basic statistics buffering overlay reclassification

GIS ANALYSIS TOOLS

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

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?

QUERIESWhere are the thinnable stands?

Age 30 and Age 40 Age 30 and Age 40 and MBF 30

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

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)

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

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

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

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 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

BOOLEAN OPERATORS Venn diagrams

BOOLEAN OPERATORS

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

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 - VECTOR

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

OVERLAY TYPES - RASTER raster maps treated

as arrays of numbers to be added, subtracted, etc.

High slope (red)+

Private land (blue)

=

Potential areas for a ski resort (brown)

OVERLAY TYPES - RASTER

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

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

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

RECLASSIFICATION results usually in a lower number of classes

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

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