Spatial Analysis and Modeling
GEO 442
1. What is Analysis?
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The process of identifying a research question
Modeling that question
Investigating model results
Interpreting the results
2. What is Spatial Analysis?
• Same process but with spatial data
• Example: Topological overlay
An analysis procedure for determining the
spatial coincidence of geographic features
3. What is modeling?
• A representation of reality used to
– simulate a process
– understand a situation
– predict an outcome
– analyze a problem
• A model is structured as a set of rules and
procedures
4. What is Spatial Modeling?
Use geographic data to;
describe,
simulate,
or predict real-world problems or systems.
3 categories of spatial modeling
• these can be applied to geographic features
within a GIS:
– geometric models, distance between features,
generating buffers, calculating areas and
perimeters
– coincidence models, such as topological overlay
– adjacency models (pathfinding, redistricting,
and allocation)
5. Two spatial models for storing geographic d
• Raster data model - matrix of square cells
• Vector data model - data stored as coordinates.
• Similar, represent a layer or set of geographic
features like points, lines, and polygons.
• Different in the way they model or represent
spatial data.
Vector data model
• Point, line and polygon objects on a map are stored as as a
collection of x and y coordinate pairs in a table.
• The x and y coordinates represent the point’s distance from an
origin point.
• Points stored as a single pair of x and y coordinates
• Lines, store the x and y coordinates of the beginning point
(from node) of the line and the end point (to node) of the line.
• Curves or changes in direction - series of x,y coordinate pairs,
(vertices), at each direction change between the beginning
point and end point of the line.
• Area (polygon) - enclose it with a line, making the beginning
and ending points of the line equal.
• Polygons which share a boundary are called adjacent.
The diagram below shows how real-world objects can be represented on a
computer monitor by x,y coordinates.
The coordinate pairs 1,5 3,5 5,7 8,8 and 11,7 represent a line (road)
The coordinate pairs 6,5 7,4 9,5 11,3 8,2 5,3 and 6,5 represent a polygon
(lake).
The first and last coordinates of the polygon are the same; a polygon
always closes.
To keep track of many features, each is assigned a unique identification
number or tag.
Then, the list of coordinates for each feature is associated with the
feature’s tag.
The objects you see in a vector theme are actually saved in the theme
table
Raster data model
• Location is the main focus of representing
geographic features.
• Earth is treated as one continuous surface.
• Each location is represented as a cell.
• Cells are organized into a matrix or rows and
columns called a grid.
• Each row contains a group of cells with values
representing a geographic phenomenon.
• Cell values are numbers, which represent nominal
data such as land-use classes or elevation.
• Cells are identified by their position in the grid. Notice
that in a grid, cells have eight (8) neighbors (except
those on the outside edges); four at the corners and
four at the sides.
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Like the vector data model, the raster data model can represent
discrete point, line and area features.
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A point feature is represented as a value in a single cell, a linear
feature as a series of connected cells that portray length, and an area
feature as a group of connected cells portraying shape.
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Because the raster data model is a regular grid, spatial relationships
are implicit. Therefore, explicitly storing spatial relationships is not
required as it is for the vector data model.
Main component of spatial analyst is the grid theme
(raster data model)
6. What is a grid theme?
• A grid divides geographic space into uniform
blocks called cells.
• Used to represent terrain elevation or other
phenomena that change gradually across a
surface.
Elevation grid looks smooth, but, as the zoomed-in graphic at the bottom
indicates, it's really composed of thousands of small cells. Each cell,
stores an elevation value for the space it covers (about 16,000 square
feet per cell for this grid.)
Two types of grids:
• Integer grids store cell values as integers
• Floating-point grids store values with decimal
points
7. What is a Surface?
• Grid themes represent a continuous surface
• Continuous data, such as elevation or air
temperature over an area.
• Surfaces can be represented by models built from
regularly or irregularly spaced sample points on
the surface (Interpolation).
• The top graphic below shows a set of sample elevation
points used to generate a surface model.
• The bottom graphic shows a spatial model actually
created from the points.
8. Using Spatial Analyst Extension
Creates, queries, maps and analyzes data
that form continuous geographic
surfaces.
Elevation
Air temperature
Precipitation
Chemical concentrations (pollutants)
Map Algebra
• Uses math-like expressions that return numeric
values to an output grid.
• Expressions are entered into the Map Calculator
in the Avenue syntax.
Querying Grids
• Select areas spatially by defining a Boolean query
based on the values of one or more grid themes.
• Output will be a grid theme with areas that match
the query given a value of 1 (TRUE) and areas that
do not match the query given a value of 0 (FALSE).
Classification
• Ordering a theme's data values into a specified
number of groups according to a particular method.
• The values in the classified theme are not changed
in any way.
• Floating point grid theme - default classification
method is Equal Interval, can be changed to
Standard Deviation.
• Integer grid theme - can be classified by any of the
five methods available: Equal Area, Equal Interval,
Natural Breaks, Quantile, or Standard Deviation.
Contours and Surfaces
• Can create isolines (a line theme) or a continuous
surface (a grid theme) using a point theme of
sampled points.
• Both help analyze continuous change of an
attribute over space (elevation, temperature, soils
pH level).
Cost surface
• Grid defining the impedance, friction, or cost to
move through a cell.
• Used to determine the least cost path between
a source and destination (travel time, dollars,
fuel).
Proximity Analysis
• Analyze the distance between features, find the
closest feature in another theme
• Create discreet distance buffers to find features
within a distance of other features.
• A buffer is a zone of specified distance around a
feature.
Overlay Analysis
• Compare two or more themes (layers) to reveal
new relationships between features in the different
themes.
• New grid theme that contains only the features
that meet the requirements of your query.
• Map Query - ( [ Landuse . desc] = "Agr" ) and (
[Flood Zone] = 1 )
Visualization
• Visualization techniques are used to create
topographic and thematic maps, statistical graphs
and to visually render surfaces.
• Hillshading - visualization tool to display hills and
valleys in relief. Calculates the effects of illumination
on a surface
• Histograms - another important visualization tool
available. A histogram is a chart of the distribution of
cell values in a grid theme. Useful to see if the values
are skewed to one side of the mean or normally
distributed.
9. Extending - Spatial Analyst Chapters
1. Start ArcView
2. Choose spatial analyst extension (file - extensions)
3. Notice how ArcView interface changes
2 new menus (Analysis and Surface)
Histogram button
Contour tool
4. Navigate to extending ArcView datasets (c:\extend)
to begin exercises
5. Answer questions for Chapters 8 - 14
Spatial Analysis
• In order to solve any problem by
Geographic information System (GIS)
modeling a series of steps must be followed
• These steps are typical for addressing any
problem with some difference in details for
each problem domain
Spatial Analysis
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Single layer operations (proximity)
Multiple layer operations (Union, Intersect)
Network analysis (shortest path)
Surface analysis (TIN, Aspect, Slope)
Grid analysis (flow direction, diffusion)
Steps for Spatial Analysis
• Establish analysis objectives and criteria
• Prepare data for spatial analysis (spatial +
attribute)
• Perform spatial operations (buffering,
overlay, feature extraction)
• Perform tabular analysis using arithmetic
and logical operations;
Reselect
Buffer
Intersect
Erase
Flow chart for database
Digitisation
AutoCAD
Import to ARC/INFO
Create topology
Build and Clean
Check feature
accuracy
Attribute
dBASEI
V.
Transform to realworld co-ordinates
Geographic database
Spatial analysis
ArcView
shape files
A system
Steps for Spatial Analysis- Continue
• Evaluate and interpret the results (validity
and checking by producing plots and
reports)
• Refine the analysis by identifying the
shortcomings and limitations of the
analysis
• Produce final maps and tabular report of the
results.
Example for spatial analysis
Finding suitable dumping site
How can I find a suitable
dumping site, that is
economically,
legally, and
environmentally
sounded?
Find a suitable dumpsite using GIS
Factors to be considered
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Groundwater contamination
Surface water contamination
Soil contamination
Water and air quality
Noise pollution
Human health due to methane and carbon
Marine environment
Dumping site
Economy
Atmosphere
Surface water
Legality
Environment
Water
Soil
Groundwater
Biotic life
Data collection
Spatial + Attribute data
• Geology, Groundwater
• Rivers, Coastal line
• Soil, Landuse
• Airport, Roads
• Settlements, Hotels
Steps for data preparation
Digitization under
AutoCad
Import to ARC/INFO
Create topology
Build and Clean
Check feature
accuracy
Transform to real
coordinate
Add attribute data
Geographic database
Geographic analysis
ArcViewshape files
Feature extraction from a GIS database
• Feature extraction from a GIS database can
be done using commands such as CLIP,
ERASE, IDENTITY, and RESELECT.
• Logic such as SELECT, ASELECT,
NSELECT and boolean operators (= , < >,
>, <, >=, <=, EQ, NE, GT, LT,GE, LE, CN,
IN).
• These commands can be used to identify
areas that met the desired criteria.
Perform spatial operations
• Feature extraction from a GIS database
(Reselect)
• Map overlay (Intersect, Union, Mapjoin)
• Proximity searches (Buffering)
Geographical objects
Landuse
Topography
Soil type
Utility
Rivers
Roads
District
Lots
Example Project Steps
Layer 1:
Lake
Layer 2:
Forest
Layer 3:
Soil Drainage
Spread
Recode
Layer 4:
Loggable
Species
Recode
Layer 6:
Near Lake
Recode
Layer 7:
Away From
Lake
Layer 5:
Drained Soils
Recode
Layer 8:
Species And
Soils
OverLay
Layer 9:
Loggable
Sites
Produce final maps and
tabular report of the results
System design
Suitable zones
Reselect Buffer
Geology Roads
Land use Rivers
Soil
Rainfall
User interaction
Intersect
suitable zones
for each factor
The best zones
User interaction
Select suitable layer for dumping:
Geology
B1
C2
C3
D3
D4
Rainfall
2420
2440
2460
2480
Productivity
2500
4000
6000
Land use
Getah
Kelapa
Padi
Pekan
Final zones
Help
Data about geology
Screening
Example for groundwater selection
Confirmation of the selection
Suitable groundwater zones
Unsuitable zones around rivers
Spatial Modelling
Step 1: State your research question(s). Then create a
flowchart to organize the data and analyses that you
will perform to explore/answer your research
question(s) (I will give you an example flowchart).
The following is an example of a research
project with a sample flow chart
 Your city is looking into alternative energy sources
that will provide clean and inexpensive power for
residents. The city has decided to look into solar
power since coal pollutes, oil may run short,
nuclear is hazardous.
 Your data set consists of elevation points and
power lines.
 You need to generate a list of criteria in aiding you
in this siting problem.
To do so you use this diagram:
The list of criteria you develop define your spatial
model.
Some spatial analysis problems can be very
complex, involving many data sets and processing
tasks.
It is often helpful to create a flowchart of the
analysis to organize the data and tasks.
The flow chart outlines the solar energy station siting
model that would be performed in this research project: