Geography 465

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Geography 465

• Overview
• Geoprocessing in ArcGIS

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Geoprocessing as modeling
MODELING
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Types of Models in GIS (by function)

• Descriptive models database
• Change models before and after
• Impact models what happens
• Explanatory models process influence
• Predictive models what will be like
• Prescriptive models should be like

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Example of Suitability Model
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The core of Geoprocessing

• building data processing chains in GIS
• data -gt operation -gt output

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Geoprocessing Framework in ArcGIS 9.x

• Multiple ways to do geoprocessing in ArcGIS

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Developing Geoprocessing Procedures with Model
Builder

• Why use Model Builder?
• Automates geoprocessing workflow
• Portability
• Extensibility
• Reusability
• Documentation

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Developing Geoprocessing Procedures (models) with
Model Builder

• Identify the components of a model
• Build and test models
• Edit existing models
• Simplify complex models using submodels
• Set up a model to run from its dialog
• model parameterization
• Facilitate conditional processing (branching)
  with scripts
• Calibrate and validate

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Model Components

• In ModelBuilder, models are represented as flow
  charts with distinct symbols for each type of
  component
• Elements are connected together via connector
  lines that serve to create processes as well as
  show processing flow

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Model Components (elements)

• Data
• Tool
• Derived data
• Value
• Derived value

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Data Process

• Models typically contain several processes, and
  they can be chained together so that the derived
  output from one process becomes the input for
  another process

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Variables

• Any element in a model that isn't a tool is a
  variable (project data, derived data, values,
  derived values)
• Variables can be thought of as placeholders for
  datasets or tool parameters
• Variable values can be easily changed, and they
  can be shared between processes in a model

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Running a Model in ModelBuilder

• To run a model is to run all of the processes
  that compose it. The readiness of a process to
  run depends on the state of its elements.
• A process can be in one of three states
• not ready to run,
• ready to run, or
• has been run.

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Sources of Simple Errors in Models

• A model's readiness to run can be affected by
  various factors. One factor is connectivity. A
  tool that is not connected to an input element
  will not be ready to run.

In this example, there is no input to the Buffer
tool operation therefore, it is not ready to
run.
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Sources of Simple Errors in Models
Another factor affecting to ability to execute a
process in ModelBuilder is specification.
Although the input data element is ready to run,
the parameters of the Add Field tool have not
been defined therefore, the process as a whole
is not
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Sources of Simple Errors in Models
The third factor affecting the ability to run a
process is data accessibility.
In this example, the elements are connected and
their parameters are fully specified. The problem
is that ModelBuilder cannot find the input data
it needs.
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How to start building a model?

• Identify functional relationships between the
  phenomenon and its variables
• Identify the initial input variables
• Identify the intermediate input variables.
• Choose appropriate tools for implementing
  transformation functions as processes
• Combine processes based on cause-effect
  relationships

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Parametrizing Geoprocessing Models

• Model variables can serve as model parameters.
  There are two purposes for this
• first, to be able to run your model from a
  dialog, and second,
• to be able to incorporate submodels.

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Parametrizing Geoprocessing Models

• Declaring a model variable as a parameter is
  called exposing the variable.

Any variable in a model (in other words, datasets
and tool values) may be exposed as a model
parameter.
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Running a model with parameters

• Right-click a data element to make it a
  parameter
• Input or output data can be parameters

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Setting model properties

• Choose Properties on a models context menu

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Setting model properties General

• Modify the name, label, description, and style
  sheet

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Setting model properties Parameters

• Add, remove, or change the order of exposed
  parameters

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Setting model properties Environments

• Set values for all environments applied to
  entire model

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Models and Submodels

• Using submodels allows you to divide parts of a
  larger model into smaller, more manageable
  pieces.
• Before a submodel can be added to a primary
  model, the output variable of the submodel must
  be exposed as a model parameter. This will allow
  the output variable to be shared between models.

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Models and Submodels
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Turning a Script into a Tool

• Another way of using a submodel in a model is to
• 1) export the submodel into a script,
• 2) turn script into a tool, and
• 3) use a script tool in a model

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Turning a Script into a Tool

• export the submodel into a script

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Script from previous export
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Add a loop wrapper
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Turning a Script into a Tool

• Steps
• 1) expose inputs and the output as model
  parameters
• 2) export the model into a Python script
• 3) turn the script into a geoprocessing tool
• 4) use the script tool as a submodel in an
  extended site suitability model

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Geoprocessing Models as Simulation Tools

• Using a model as a simulation tool requires
  exposing the output data set as a model parameter
• Dialogs provide a simplified view of a model and
  allow the user to easily change parameter values
  each time the model is run.
• Once these model parameters are set, model users
  can simply use the dialog for execution.
• Running a model from its dialog allows for easy
  testing of alternative scenarios.

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Sequence Control and Conditional Processing in
ModelBuilder

• You can control the sequence of processing in
  your model by applying a precondition (the output
  data from one tool must exist before the tool can
  be executed)
• You can build conditional processing (branching)
  into your model with Python scripts
• Python Exercise time!