Defining Constraints

Constrain areas from development in scenarios.

Constraints are areas that cannot receive development in scenarios. Any spatial layer can be used as a constraint, and each scenario in a project can use a unique set of constraints. This article provides a conceptual overview of constraints, and steps on how to define and apply, or remove, them.

Constraints Overview

Any layer in your project can be used as a constraint. This can include layers for environmentally sensitive areas or other reference data layers added via the Layer Manager, or custom layers that you upload. Constraint layer features may be points, lines, or polygons. Applying a layer as a constraint constrains the entirety of any features (parcels or blocks) in a scenario canvas that spatially intersect with the constraint layer features. Scenario canvas features are either constrained or not; they cannot be partially constrained.

Constraint effects are indicated in paint selections

Using Filtered and Buffered Layers as Constraints

All features within a constraint layer are applied as constraints. If you want to use only a selection of features as constraints, you'll need to first create your selection and save it as a filtered layer (see Filtering and Joining Data for details), then use the filtered layer as the constraint layer. Similarly, if you want to constrain a buffered area around your constraint features, you'll need to create and save a buffered layer (see Creating Buffered Layers for details) to be used as the constraint layer.

Managing Constrained Features

When a scenario canvas feature is constrained, its population, housing, jobs, and development attributes are all set to zero -- even if development existed there in the Base Canvas. Constrained features are restricted from receiving scenario growth. The scenario painting selection control will indicate the amount of constrained area, if any, within the features you have selected to paint. While they cannot receive development and associated population, housing, and jobs, constrained features can be painted, though only in terms of a land use type name (and consequently its associated land use categories).

Individual constraint layers can be turned off at any point, including after scenario painting. The effect of turning off a constraint layer depends on whether previously constrained features have been painted or not:

  • If a feature was not painted with a new land use type while constrained, then population, housing, jobs, and development attributes are reverted to the base condition.

  • If a feature was painted with a new land use type while constrained, then population, housing, jobs, and development attributes are updated in accordance with the new land use type -- the equivalent of a fully executed paint on an unconstrained feature.

In working with constraints, it's helpful to remember that you can always revert features in a scenario canvas to their base condition, provided they are no longer constrained. If needed, you can select constrained or previously constrained features in your scenario canvas by applying a join filter with the layer used as a constraint (see Filtering and Joining Data for details on using join filters). Keeping these mechanics in mind may help you in structuring your scenario development workflow.

Maintain any layers that have been added as constraints; removing or deleting them from your project will hinder you from being able to select constrained features in the scenario canvas.

How to Define Constraints

To define constraints:

1. Add or upload the spatial layer to be used as a constraint. You can use any layer as a constraint. If you want to use only a selection of features from a layer as constraints, first save your selection as a filtered layer (see Filtering and Joining Data). If you want to constrain a buffered area around your constraint features, create a buffered layer (see Creating Buffered Layers).

2. Roll over the desired layer in the Layers list and click the Open menu button. The Layer Options menu appears.

3. Select Add to Constraints. The layer is added to your project's Constraints list. The Constraints list is accessed through the Constrain tab of the Layer Details pane for a scenario canvas layer -- we'll go there next.

4. Activate the scenario canvas layer of the scenario in which you want to apply the constraint. If you want to apply the same constraint in multiple scenarios, you'll need to follow the steps below for each scenario.

5. Click the Constrain tab. You will see a list of all layers that have been added as constraints within your project.

All scenarios contain the same list to choose from. However, scenarios can differ in terms of which constraints are applied.

6. Click the checkbox for any layer that you want to apply as a constraint in the current scenario. You can select one or more.

7. Click Apply Changes. UrbanFootprint will update your scenario canvas to reflect the constraints. This may take some time depending on the number of features affected.

You will see the effects of your constraints upon selecting constrained features when you paint scenarios. If you are applying constraints to features that have already been painted in a scenario, their values for population, housing, jobs, and development attributes will be set to zero. Any changes will be reflected in updated scenario totals.

Applying changes to constraints (whether adding or removing) is a scenario processing operation. Any analyses that have been previously run on the scenario will be rendered out of date, and will need to be re-run to reflect changes.

How to Remove a Constraint

Constraints can be deactivated for individual scenarios, or deleted completely from a project. To turn off a constraint for a scenario:

1. Activate the scenario canvas layer of the scenario for which you want to turn off the constraint.

2. Click the Constrain tab. You will see a list of all layers that have been added as constraints within your project.

3. Click to deselect the checkbox for any layers that you want to turn off as constraints in the current scenario. You can select one or more.

4. Click Apply Changes. UrbanFootprint will update your scenario canvas to reflect the removal of the constraints. This may take some time depending on the number of features affected. Turning off a constraint layer can have either of the following effects:

  • If a feature was not painted with a new land use type while constrained, then population, housing, jobs, and development attributes are reverted to the base condition.

  • If a feature was painted with a new land use type while constrained, then population, housing, jobs, and development attributes are updated in accordance with the new land use type -- the equivalent of a fully executed paint on an unconstrained feature.

You will see the effects of removing constraints reflected in scenario totals for population, housing, jobs, and development attributes.

Removing constraints is a scenario processing operation. Any analyses that have been previously run on the scenario will be rendered out of date, and will need to be re-run to reflect changes.

How to Delete a Constraint

A constraint can be deleted from your project so long as it is not active in any scenarios. To delete a constraint from a project, first turn it off for all scenarios, then:

1. From the Constraints List, open the Constraint Options menu for the layer to be deleted.

2. Select Delete. A confirmation window will appear.

3. Click Submit to confirm removal. The constraint will be removed from all scenarios in your project.

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