Spatial Analysis and Modeling

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Spatial Analysis and Modeling

• GEO 442

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1. What is Analysis?

• The process of identifying a research question
• Modeling that question
• Investigating model results
• Interpreting the results

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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

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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

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4. What is Spatial Modeling?

• Use geographic data to
• describe,
• simulate,
• or predict real-world problems or systems.

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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)

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5. Two spatial models for storing geographic data

• 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.

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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 points
  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.

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• 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.

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To keep track of many
features, each is assigned a unique
identification number or tag. Th
en, the list of coordinates for each feature is
associated with the features tag. The objects
you see in a vector theme are actually saved in
the theme table
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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.

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• 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.
• 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.

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Main component of spatial analyst is the grid
theme (raster data model)
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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.

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• 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.)

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Two types of grids

• Integer grids store cell values as integers
• Floating-point grids store values with decimal
  points

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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).

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• 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.

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8. Using Spatial Analyst Extension

• Creates, queries, maps and analyzes data that
  form continuous geographic surfaces.
• Elevation
• Air temperature
• Precipitation
• Chemical concentrations (pollutants)

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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.

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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).

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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.

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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).

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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).

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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.

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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 )

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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.

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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

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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

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Spatial Analysis

• Single layer operations (proximity)
• Multiple layer operations (Union, Intersect)
• Network analysis (shortest path)
• Surface analysis (TIN, Aspect, Slope)
• Grid analysis (flow direction, diffusion)

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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

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Reselect
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Buffer
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Intersect
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Erase
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Flow chart for database
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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.

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Example for spatial analysisFinding suitable
dumping site

• How can I find a suitable
• dumping site, that is
• economically,
• legally, and
• environmentally
• sounded?

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Find a suitable dumpsite using GIS
Factors to be considered

• Groundwater contamination
• Surface water contamination
• Soil contamination
• Water and air quality
• Noise pollution
• Human health due to methane and carbon
• Marine environment

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Data collection
Spatial Attribute data

• Geology, Groundwater
• Rivers, Coastal line
• Soil, Landuse
• Airport, Roads
• Settlements, Hotels

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Steps for data preparation
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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 ( , lt gt, gt, lt, gt, lt, EQ,
  NE, GT, LT,GE, LE, CN, IN).
• These commands can be used to identify areas that
  met the desired criteria.

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Perform spatial operations

• Feature extraction from a GIS database (Reselect)
• Map overlay (Intersect, Union, Mapjoin)
• Proximity searches (Buffering)

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Geographical objects
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Example Project Steps
Spread
Recode
Recode
Recode
Recode
OverLay
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Produce final maps and tabular report of the
results
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System design
Suitable zones
Intersect suitable zones for each factor
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User interaction Select suitable layer for
dumping Geology Rainfall Productivity
Land use B1 2420 2500 Getah C2
2440 4000 Kelapa C3
2460 6000 Padi D3 2480 Pekan
D4
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Data about geology
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Screening
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Example for groundwater selection
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Confirmation of the selection
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Suitable groundwater zones
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Unsuitable zones around rivers
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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).

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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.

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To do so you use this diagram
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• 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.

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The flow chart outlines the solar energy station
siting model that would be performed in this
research project