the model builder

DCP 2002: Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning , UF

THE MODEL BUILDER

week 7


topics of the week

What is a model

Computer simulation models

Model Builder in ArcGIS

Model Builder’s interface

Using the Model Builder


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?


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


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)


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


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.


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


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


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.



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.



Open ArcToolbox.

Right-click in a blank area in ArcToolbox

Choose Add Toolbox

Right Click on the new Toolbox

(FireTools)

Click New > Model




Before starting your model, save it, name it, and set any of

the appropriate properties.


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.



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

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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.


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

the model builder

Documents