Concept of Keys
Consider the following example:
Water Overlays require an attribute to identify Weirs.
The Water Overlay has named this attribute that it expects: the Weir height.
This expected attribute is known as a Key.
Next, let us assume that the Weir's data is supplied by a user.
In the data, the weir's height is described by the attribute HEIGHT_OBJ.
The Overlay Weir Height Key can be set to HEIGHT_OBJ.
This way, when the Water Overlay wants to obtain the Weir Height value of a construction, they can use the attribute HEIGHT_OBJ, which it had stored for the WEIR_HEIGHT key.
How to adjust Keys
The Keys an Overlay's calculation model uses and their configured values can be found under the tab Keys in the right panel.
Additionally, some Overlay Wizard, such as the Water Overlay Wizard, allow users to set the Key's relevant to the context of the wizard's step. For example, Weir relevant Key's WEIR_HEIGHT, WEIR_WIDTH, WEIR_ANGLE and WEIR_COEFFICIENT can be set in the Weir Step of the Water Overlay Wizard.
Some keys have an additional role; They are used by an Overlay to identify if a component, such as Building or Area, belongs to a certain group.
For example, the WEIR_HEIGHT key is used to place Buildings that have this attribute into the Weir group. The Building therefore takes the role of a Weir. Depending on the underlying calculation model of an Overlay, a component such as a Building can only be assigned one role.
When a component has more than one identification Key, such as WEIR_HEIGHT and CULVERT_DIAMETER, the Building is assigned the role with the highest priority, which is determined by the calculation model. In the case of the Water Overlay, Weirs are prioritized above than Culverts.
In this case the Water Overlay Wizard will also provide an Identification warning in the Culvert's wizard step: "Warning: Building is already recognized as a Weir".