Understanding model layers

The four tabs on the left side of the window give you access to the different layers of the model: Interface, Map, Model, and Equation. Each layer provides you with a different aspect of designing and presenting a model.

• Interface layer – Use this layer to create engaging end-user interfaces for your models. For example, you can use the Interface layer to create a "flight simulator cockpit" where users can interact with the model as the simulation progresses. The Interface layer makes it possible for you to transform a model into a compelling environment for learning.

• Map layer – Use the Map layer to lay out your thinking in the form of a high-level map. During the mapping phase, you identify the key entities in your model and organize them in relation to each other. When you view your model on the Map layer, you are looking at the overall flow and design of the model. You can also use the Map layer to provide high-level documentation about the model by using the Documentation panel. When you're ready to specify detailed properties for the model (for example, initial values and equations for each building block), you move to the Model layer.

  Note: When you start iThink or STELLA, the software opens to the Map layer.

• Model layer – Use the Model layer to transform maps into models that can be simulated on your computer. The Model layer is often referred to as the "engine room" for the models you create. When you work on the model layer, you specify the details of how the entities interact with each other, the initial values or equations for building blocks, and other detailed properties that control how the model functions when the simulation runs.

• Equation layer – Use this layer to view a list of all the equations that make up your model. You can also use this layer to delete model entities by deleting their associated equations.

  Note: The equations you see on this layer are created automatically and are not editable here. To edit equations for a specific entity, use the Equation panel.

This multi-layer design makes it easy for model builders to manage the visual and conceptual complexity of the model by dividing different aspects of the model into different layers: the Map layer gives you a place to lay out your thinking; the Model layer gives you a place to define detailed model structure; the Interface layer allows you to focus on how to present the model to users and how to provide them user input/output access to the model; and the Equation layer allows you to see all the equations at work in the model in a single place.

For model users, separate layers make it possible to unravel the intricacies of the model in "mind-size bites." They can investigate the model layer by layer and focus on only one aspect at a time.

To learn how to navigate from layer to layer in your model, see Navigating between model layers.

See Also