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Model parameters

Release 9.3
Last modified January 26, 2009
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When you open a tool dialog, you see all the tool's parameters. Each parameter has a user interface control, referred to as the parameter control, that helps you enter a value for the parameter, such as a drop-down list or a browse to disk button.
Learn more about tool dialogs and parameter controls.

The models you create are tools, and as such, they have parameters that will be displayed in their tool dialog when opened from ArcToolbox or ArcCatalog. When you are building a model in ModelBuilder, it is up to you to choose which variables become parameters the user will see when they open the model's tool dialog. These parameters are called Model Parameters.

It's not necessary to expose any variables as parameters. You can always make a model that contains all the information it needs to run without any user intervention. When a model does not expose any parameter, the model tool's dialog will look like this:

A model tool that hasn't exposed any parameters

This is not an error (although it is often mistaken as one) and you can execute the tool by pressing OK. However, you typically do want to expose some model variables as parameters.

To expose a variable as a parameter in ModelBuilder, right-click the variable and click Model Parameter. The letter P will appear by the variable to indicate that it is now a parameter and will be present on the tool dialog. Creating a simple model demonstrates this.

If you have a nonempty variable (the oval is not white) that is exposed as a parameter, when you open the tool dialog, the value of that parameter will be displayed. This is how you provide a default value for the parameter. If the variable you expose is empty (the oval is white), the tool's parameter control will be empty as well, and the user will be expected to provide a value.

You should only expose parameters that the user needs to provide or alter. There is no need to expose every variable as a parameter.

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