International Layer Standards
Globally there are various CAD layering systems available which are often built into the CAD and BIM software available, and these generally include implementations based upon:
- BS 1192 (British Standard
- AIA (American Institue of Architects)
- CP 83 (Singapore)
- ISO 13567 (International Standards Organization)
Users of BIM software often state that they do not use layers. However, whenever they export to IFC, DWG or DGN etc then the settings will often define the layer standards to be used. Settings for export should be configured to the appropriate layer standard.
BS1192:2007 Layer Fields Explained
The UK approach to layering was traditionally based upon BS 1192-5:1998 which was then incorporated into the BS 1192:2007 standard. The BS 1192 approach used a variable length field generally using a hyphen as the main field separators and an underscore to separate the Alias or description.This was different to the ISO 13567 approach which used fixed field lengths and no seperators.
There have been differing implementations of BS 1192 over the years using alternate classifications selected. The typical approach developed by CPIC included Uniclass 1.4 Classification and the implementation of the following fields:
| Field | Role | Delimitor | Classification / Element | Delimitor | Presentation | Delimitor | Alias |
| Name | A | – | G23 | – | M2 | _ | Stair |
| Example | Architect | Stairs (Uniclass) | 2D Model Graphics | Text |
There is often misunderstanding regarding the definitions of the various fields within BS1192;2007 and other standards, with some implementations increased this misunderstanding. There is a brief discussion below regarding how the fields in BS1192 are intended for use to ensure true compliance.
‘Role Field’
‘The Discipline who is the owner of the information’
This is a single Character code representing the role of the creator of the data produced. BS1192:2007 provides a list of the disciplines which has been replicated in this document.
There are specific implementation differences between fields such as ‘Role’ in the UK and ‘Agent Responsible’ from ISO 13567 or ‘Discipline Designator’ from the AIA CAD standards. Within BS1192:2007 the ‘Role’ field signifies the Author or Owner of the information. Therefore when an Architect draws a column the layer ‘Role’ field must be designated with the letter A for Architect. In the AIA CAD standards the Layer Field refers to the ‘Discipline’ having responsibility for the object. So in the USA the Architect would draw a column and the ‘Discipline’ field would be designated S, passing the responsibility to the Structural Engineer.
In the UK each discipline only draws on the layers where the Role Field designates their specific discipline. Therefore anything an Architect draws must be drawn on a Layers commencing with the letter A.
The following Role table is taken from BS1192:
| CODE | Role |
| A | Architects |
| B | Building Surveyors |
| C | Civil Engineers |
| D | Drainage Sewage and Road Engineers |
| E | Electrical Engineers |
| F | Facilities Managers |
| G | GIS Engineers & Land Surveyors |
| H | Heating & Ventilation Engineers |
| I | Interior Designers |
| K | Client |
| L | Landscape Architects |
| M | Mechanical Engineers |
| P | Public Health Engineers |
| Q | Quantity Surveyors |
| S | Structural Engineers |
| T | Town & Country Planners |
| W | Contractors |
| X | Sub-Contractors |
| Y | Specialist Designers |
| Z | General (Non disciplinary) |
A Hyphen (-) is used as a separator between the Field 1 Role and Field 2 Classification.
Classification / Element Fields
BS1192:2007 mandates the use of Uniclass as the classification system to be used within Layer names. The original implementation of the Element fields within Uniclass meant that often the use of concatenated Uniclass codes was required in order to classify specific elements.
CPIC have therefore carried out additional work within this area and published version 1.4 of Uniclass specifically to support the Layer Generator. This unified tables G (Elements for Building) and H (Elements for Civil) into one combined table to enable the classification of elements across both Building and Civil, whilst also removing the need for concatenated codes. There has also been work on Table Z which provides a table for CAD specific classifications.
CPIC Uniclass 1.4 Implementation was developed to support Layer implementations. BUMuk provided a supporting document as below to support the implementation:
NBS in 2013 then developed initially Uniclass 2 and then Uniclas 2015, which is the latest release with tables shown and linked below. More infomation can be found from the NBS website
A Hyphen (-) is used as a separator between the Field 2 Classification and Field 3 Presentation.
Presentation Codes
BS1192 allows for a definition of the graphics to be used to represent an object in either a single or two letter codes. Where graphic representations are to be kept simple then the single codes as defined within BS1192:2007 should be used.
Where there is a specific requirement for control of more complex graphics then the following 2 letter codes may be adopted. This allows for the separation of graphics forward, below and above the cut planes as well as for hidden objects within these views as defined within BS8541-2:2011.
| Presentation Code | Description | Line Type |
| A | Annotation (Tags, Arrows, etc.) | |
| D | Dimensions | |
| H | Hatch | |
| M | Model related graphics | |
| M2 | 2D Model graphics | |
| M3 | 3D Model graphics | |
| MA | Model Analysis | |
| MC | Model Cut plane (Section / Details /Plan) | Thick Line |
| MG | Model Grids (Grids, Reference planes, Reference Lines | |
| MH | Hidden lines, Items Hidden beyond cutting plane(BS8541-2:2011 item 1.304) | Hidden line |
| MF | Model Forward. Items that need to be shown forward of the cut plane. | Fine Line |
| MG | Model grids (Grid references, reference planes, reference lines) | |
| MH | Model Hidden for Hidden lines, items hidden beyond cutting plane(BS8541-2 : 2011 item 1.304) | |
| MM | Model mirrored / reflected information (Ceilings, ductwork etc…) | |
| MN | Model Non visible elements , Behind / above cut plane(BS8541-2:2011 item 1.302) | Dashed dot dot line |
| MV | Model Visible items Behind / above the cut plane(BS8541-2:2011 item 1.301) | Dashed dot line |
| P | Plot /Page related graphics | |
| T | Text |
For Single Character codes please refer to BS1192:2007 Table 15.
An Underscore (_) is used as a separator between the Field 3 Presentation and Field 4 Alias.
Alias
Description code to assist Layer Identification
The purpose of the Alias fields is assist the identification of the building elements defined by the classification system. To ensure the consistent use of the Alias field CPIC have provided a standard list of Aliases to be used with each of the Uniclass classifications.
Note
Only the letters (A to Z), hyphen(-), underscore(_) and numbers (0-9) shall be used in the naming layers alias and the following characters MUST NOT be used:-
- ! “ £ $ % ^ & * ( ) + = < > ? | \ / @ ’ ~ # } ] ¬ ` ‘
- Spaces within an alias MUST NOTbe used.
The only special characters that should be used should be underscore “_”
Underscores are used to replace spaces within the Alias and any plurals are removed.