Expressions

When editing continuous landscape variables, like canopy cover or canopy bulk density, usually all different values of the theme will need to be changed, not just one. Expressions can be used to edit all values of a landscape theme by adding, subtracting, multiplying, or dividing all the values for a landscape theme by a set amount.

1.  In the Target Theme to Modify: list box to select the landscape theme to modify with this rule.
2. Select the Expression radio button from the Value Assignment group.
3. From the Theme list box select the landscape theme with the values to be modified. Most often this will be the same theme as the Target Theme to Modify: selection.
4. Select an operator from the Operator list box and enter a value for the operator to apply.
5. The Fuel Model Filter group is optional and discussed in the Create or Edit Rules topic. (this filter can be used even if the Target Theme to Modify: is not Fuel Model)
6. The Additional AND Clauses group is optional and discussed in the Masks topic.

An expression to raise the canopy base height by 30% will look like this.

The Rule Text at the bottom of the "Create/Edit Landscape Rule" dialog box will look like this.

Click OK to close the "Create/Edit Landscape Rule" dialog box and return to the "Landscape Editor" dialog box where the new rule is listed along with any other previously created rules.

The four commands for a rule, listed to the right of the rule description, Test, Apply, and Delete can then be used on any rule in the list.