Last edited 24 May 2019

CAD layer

A CAD layer is a component of a computer aided design (CAD) drawing file. Drawings can be organised by assigning objects to layers according to logical categories.

CAD drawings can quickly become visually complex, and difficult to structure as more objects are added. By assigning objects to different layers they can be collectively grouped, altered, moved and hidden from view as required. It can be helpful to think of layers as being the digital equivalent of clear plastic sheets that can be viewed and worked on separately, or combined to show multiple layers.

Objects can be associated by their function or location, related objects can be displayed or hidden in a single operation, and common properties such as line-type, colour, weight and so on can be enforced for each layer.

Layer properties managers can be used to organise layers. These lists the layers in the drawing, indicate current and visible layers and show layer properties. All new objects will automatically be placed on the current layer.

The default layer that exists in all drawings is Layer 0, although it is recommended that new layers are created rather than building a drawing solely on this layer. It can be useful to create a layer for drafting construction and reference geometry and other notes/calculations that will be kept hidden when viewing all the layers together and won’t be printed. It is also generally recommended that hatches and fills are contained on the same layer, allowing them to be turned on or off in one action.

It is possible to:

  • Turn off layers: Layers can be turned off to reduce the complexity of the drawing.
  • Freeze layers: Layers that do not need to be accessed can be frozen, which improves the performance of very large drawings.
  • Lock layers: This prevents changes to the objects on a layer being made accidentally. These layers are faded rather than hidden completely.
  • Set default properties: Default properties can be created, such as colour, linetype, lineweight, transparency, and so on.

When working on a project, it is important that everyone conforms to the same layer standards, as this enables the organisation of drawings to be more logical and consistent, as well as easier to share, collaborate and maintain over time.

A standard set of layers can be saved in a drawing template file as to be easily accessible. Standards such as AEC (UK) CAD Standard, BS EN ISO 13567-1:2017 or BS1192 might be used (now superseded by ISO 19650).

NB: BS 1192:2007+A2:2016 Collaborative production of architectural, engineering and construction information. Code of practice, (now replaced by BS EN ISO 19650) describes a layer as a ‘..container comprising selected entities, typically used to group for purposes of selective display, printing and management operations.’

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