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DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
THE MODEL BUILDER
week 7
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
topics of the week
What is a model
Computer simulation models
Model Builder in ArcGIS
Model Builder’s interface
Using the Model Builder
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
A model is an approximate substitute for a real system. It is a human construct to help us better understand world systems.
Example of a model – building plans
Key features in the development of a model
a goal must be clear
initial criteria must be identified for reaching that goal
simplifying assumptions must be made
the range of applicability of the model should be understood
limitations of data/parameters must be known
What is a model?
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Computer simulation models
A special category of models – computer simulation models
calculations are turned over to computers
the logic of the model’s construct remains with us
the flow of the processes can be automated – not always
they facilitate experimenting
they facilitate re-runs
they are easier to be modified, tweaked, expanded
they are easier to be shared and examined
they facilitate documenting processes and parameters
they increase our understanding of the system
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Main elements of a computer model
Data
Input data
Intermediate data
Output data
Overall process flow, or logic of the model, or step by step operations
Functions/algorithms implemented during the process (buffer a road, or select parcels)
Parameters (100 m buffer, or parcels < 5 acres)
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Parcels
Census Blocks
Major Roads
Scenic Roads
Vacant Parcels
Targets
Highways
Scenic Buffer
Target Parcels
Final Parcels
Highway Buffer
Select ‘Vacant Residential’
Select P019002 >= 25
Select CLASS = ‘Interstate or ‘US Roads’
Buffer 1km
Buffer 1/2km
Select Parcels Containd within the block
Select Parcels within buffer
Select Parcels within buffer
Example from our Suitable Location Exercise 8
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Limitations of models
They represent the real world i.e. are inherently inexact.
The input data can be inaccurate.
The logic of the process flow can be imperfect.
The individual functions used may be inappropriate.
The parameters used may be uncertain as they are usually determined empirically.
Any or all of the above.
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Model Builder is an environment in ArcGIS that allows for constructing a GIS based computer model.
Other GIS software may have other environments that provide similar capability.
Model Builder allows for a sequence of geoprocessing operations to execute automatically, and to generate a final dataset output.
It allows for modification/change of all the model’s elements i.e. the model can be refined an re-run to produce alternative outcomes.
What is Model Builder
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
ModelBuilder’s interface is a graphical environment for creating and interacting with the model.
The white empty background is called canvas.
The main building block of a model is called a process. A process consists of a geoprocessing tool.
The individual parts are called elements.
All elements, when tied together with connectors, make up the model diagram.
The Model Builder Interface
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
The model diagram shows all the processes and the sequence in which they run. The connecting arrows show how elements and processes are related to each other.
The Model Builder Interface
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Basic idea is that of a dependency diagram
User specifies inputs, processing, and outputs
If inputs change, system repeats intermediate operations with new inputs
The diagram has three kinds of elements
Inputs
Geoprocessing operations
Outputs
Output from one operation can be used as input to the next, allowing for chaining
Connector arrows show direction of processing.
The Model Builder Interface
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Open ArcToolbox.
Right-click in a blank area in ArcToolbox
Choose Add Toolbox
Right Click on the new Toolbox
(FireTools)
Click New > Model
Using the Model Builder
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Using the Model Builder
Before starting your model, save it, name it, and set any of
the appropriate properties.
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
To build a model, you drag tools from the appropriate toolbox into the
model.
Then click on the tool (such as Buffer), and fill in the parameters.
Drag layers from the table of content.
Finally, connect data and processing boxes together.
When you are done the elements turn blue, yellow, or green.
Using the Model Builder
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
blank or white elements are not ready to run
colored elements are ready to run
colored elements with a dropshadow have finished running
Model elements can be in one of three states:
Model Builder’s interface
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Storing and retrieving models
Models are saved in an Toolbox (new or existing) in a .tbx format.
Models are saved in a Toolbox by default under:
c:\users\Username\documents\ArcGIS
New models can be added to the Toolbox from within a project,
but they reside on disk, outside of the project.
The Toolbox can be removed from the project and added later,
or it can be saved within the project.
Models can be saved within .mxd projects in ArcToolbox or they can
be deleted from .mxd projects.
They relate to .mxd projects similarly to datasets.
DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF
Generalizing models
A few words about generalizing Models
By default, models only use exact data as originally specified To convert a model into a true “tool” we need to specify which inputs / outputs are variable parameters
Right mouse on input or output Select “Parameter” (toggle)
After Parameters are set, double clicking brings up user dialog