Using the ModelBuilder of ArcGIS 9 for Landscape Modeling

Using the ModelBuilder of ArcGIS 9 for Landscape Modeling
Jochen MANEGOLD, ESRI-Germany
Geoprocessing in GIS
A geographic information system (GIS) provides a framework to support planning tasks
and decisions, to help managing the natural and man-made environment and the resources
of the earth. With providing tools for all kind of geoprocessing, the GIS framework allows
the user to define, manage and analyze all the information used to support planning or to
make decisions.
ESRI’s ARC/INFO was built upon such a framework, using coverages as an intelligent
data model for storing geometry, topology and attributes, and offering all tools to capture,
store, and manage as well as to analyze and present landscape data. With Arc Marco
Language (AML) a scripting language can be used to store geoprocessing workflows and
dialogs.
ArcGIS 8 marked a new milestone in ESRI’s GIS client and server architecture. On the
client side, completely new software architecture, was released, built on modern GIS and
application framework components, including new applications like ArcMap and
ArcCatalog. On the server side, the Geodatabase offers a new object-relational data model
to store intelligent geo-objects with properties and behaviour in a Relational Database
Management System (RDBMS) as well as “link” those objects and layers by flexible
topological rules, thus extending the possibilities far beyond the coverage model.
ArcGIS 9, a new geoprocessing framework which includes a model builder as a graphical
environment to create diagrams of steps for complete geoprocessing tasks will be
introduced to make geoprocessing much easier, more flexible and very user friendly.
Geoprocessing Tools with ArcGIS 9
The main concept of geoprocessing is based on a concept of data transformation. A typical
geoprocessing operation takes an input dataset, performs an operation on that input dataset
and returns the result of the operation as an output dataset. ArcGIS 9 will have hundreds of
these single geoprocessing tools for processing all types of ESRI compatible spatial and
non-spatial data formats, namely coverages, shapefiles, personal and ArcSDE geodatabase
featureclasses, with CAD and VPF files, as well as tables and text files. These tools can be
grouped into different types of operations, such as data conversion, analysis or data
management.
For convenient search and retrieving, these groups of similar tools are organized in
ToolBoxes and Toolsets, which can be stored in system files or database tables. These
ToolBoxes are presented to the user as a list of his favourites in the ArcToolbox window
for easy access in the ArcGIS applications like ArcMap and ArcCatalog. The number of
potentially available tools varies, depending on the type of product license such as

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ArcView, ArcEditor or ArcInfo and the types of ArcGIS extensions like 3D Analyst or
Spatial Analyst.
Fig. 1:
ArcCatalog and the ArcToolbox window
Geoprocessing Methods in ArcGIS 9
There are four different ways to perform geoprocessing tasks in ArcGIS 9. Which method
you choose depends on which method is best suited to the particular task and your personal
preference. You can choose a dialog from the ToolBox window or use the command line
for input typing to perform a single geoprocessing task. With dialogs, the tools provide a
form, where you can specify the data and parameters for the geoprocessing operation.

Using the ModelBuilder of ArcGIS 9 for Landscape Modeling 3
Fig. 2:
The command line window in ArcMap
The command line is similar to the Workstation ArcInfo command line, where you type in
the command including all input data and parameters. The command line in ArcGIS 9
prompts you with the usage of the specified command and helps you with intellisense and
dropdown lists.
For more complex tasks or workflows, involving multiple functions, choose a model tool or
create a new model and link single processes together. To perform the same function many
times on different datasets or with different parameters, you can use or create a tool derived
from a script.
Fig. 3:
A geoprocessing script written in Python using the PythonWin IDE

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Scripting offers an efficient and effective way of managing geoprocessing needs. They
provide an environment, which makes it easy to process large volumes and quantities of
data. They are recyclable and easily modified. Any scripting language, which is COM
compliant, interacts well in the ArcGIS environment such as VBScript, JScript or Python.
Using ModelBuilder in ArcGIS 9
The ModelBuilder in ArcGIS 9 provides a graphical environment to create a diagram of
multiple steps to complete a complex geoprocessing task. The diagram you build represents
a model. Tools can be draggen from ToolBoxes in the ArcCatalog tree or from the
ArcToolbox window into the Model diagram to build the processes that make up the
model, then filled in the necessary input data and parameters for each tool and connect the
processes together. When the model is run, ModelBuilder processes the input data in the
order specified and creates output data. The model can be saved, modified and rerun.
Geoprocessing functions can be tied together in a model that keeps track of the datasets,
processes, parameters and assumptions that are used. This makes it easy to redo the exact
same procedure multiple times, or to alter data and parameters slightly.
Fig. 4:
The ModelBuilder window with a typical model

Using the ModelBuilder of ArcGIS 9 for Landscape Modeling 5
A model contains information about data, how to process the data, and the sequence of
processing. The model can be displayed as a process flow called a model diagram or as a
tool in a toolbox. A tool exposes model parameters selected by the model author and is the
common way of executing a model. In the model diagram, there are symbols, called model
elements, which represent data and tools that operate on data. The model elements are
connected together into processes. A process is a set of input data, the tool that operates on
the input data, and the resulting output data. Connector arrows indicate the sequence of
processing. There will usually be several processes in a model, and they can be chained
together so that the derived data from one process may become the input data for another
process.
The model diagram provides a graphical way to present models to decision-makers and the
public. So the ModelBuilder can be used for cartographic modeling and analysis, such as
environmental or land use modeling.
Fig. 5:
A conceptual model with different processes
Figure 5 is a conceptual overview of a model built from three processes. The processes are
built by connecting model elements representing data and functions. Each process has one
or more input datasets, a tool, and output data. Connecting the output from one process to
the input of another process chains the processes together.
In addition to the basic model elements such as input and output data, tools, and
connectors, there are text labels, which are graphical elements used to place explanatory

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text in a model. A label is not part of the processing sequence. Labels can be attached to
connectors or they can float freely in the model diagram.
Model elements have properties and connection rules that define how they behave. Data
elements have a property that describes the location of the data. Function elements have
properties that describe how to process data. For example, the Buffer function has a buffer
width property. Properties are editable through dialogs, wizards, and property sheets.
Connection rules describe what type of input each model element will accept and what type
of output it produces.
Sharing a model is as simple as sending the model file via email or publishing a ToolBox
on a server or with a web service. The receiving party simply saves the file anywhere on
their system. A user can then add the file to the ArcToolbox window for easy access. The
concept behind model sharing, or any ToolBox tool for that matter, is to maximize
resources and productivity by avoiding duplication of effort, and because it simply makes
more sense, other than from just a cost-effective point of view.
Summary
The evolution of geoprocessing has shown that there is no single user experience that
satisfies all user requirements and preferences. Early packages exposed geoprocessing
operations as a set of commands while more contemporary systems have a graphical user
interface (GUI) in which the user interacts and composes the operation to be executed. A
third method exposes the systems core functions in an application programmer interface
(API) that allows a software developer to invoke geoprocessing operations outside of the
GIS systems GUI. Each method has its advantages and disadvantages, but when all three
are supported in a GIS package, the user gets to choose which best suits his or her needs,
thereby offering the best possible user experience for the task at hand.
References
ESRI Inc. (2002): Geoprocessing in ArcGIS 9.0, White Paper
ESRI Inc. (2002): Creating a Model in ArcGIS 9.0, White Paper