# Reshaping the Digital Twin Construct with Levels of Digital Twinning (LoDT)
## 4 Assessing the Level of Digital Twinning (LoDT)
### Digital Twinning Dimensions
#### 4.2.4 Geometric Representation  
The authors consider that, in a simplified manner, there are two types of information to represent in a digital model: geometric information (such as shape, appearance, detail, position, dimensions, etc.) and non-geometric information (asset type, design specifications, materials, dates, historical records, supplier data, etc.) [95]. Each digital twinning case has a specific purpose, and that purpose should specify and justify the type of needs for both geometric and non-geometric information [79]. Both geometric and non-geometric dimensions are aligned with the concept of Level of Information Need [80], which defines the requirements for geometrical and alphanumerical information needs for BIM. The Level of Development (LOD) [88; 96] and the Level of Information (LOI) [87; 97] proposed for BIM models are conceptually equivalent to the levels of geometric and non-geometric representations in the context of digital twinning.  
Nevertheless, there are important differences that need to be addressed. While LOD and the LOI are commonly used for BIM project requirements, the levels of geometric and non-geometric representation are defined internally by the model owner to support the planning activities of the digital twinning journey. Moreover, the descriptions in the literature for the different LOD and LOI are closely related to some specific phases in the asset life cycle. However, the authors argue that the LoDT should not be directly defined by the asset life cycle phases. Instead, the life cycle phases should define the purposes that underpin the digital twinning construct, as outlined in Section 2.1. Therefore, the LoDT in terms of geometric and non-geometric information remain neutral with respect to life cycle stages, in contrast to existing proposals for LOD and LOI.  
Mapping these information needs is key to guaranteeing that they are incorporated into the model according to the identified purpose. Moreover, the representation should be \"fit for purpose\", meaning it should not be more complex than necessary, as this can lead to inefficiency and no added value [63].  
Geometric representation should align with the type of assets and the specific purpose at hand. In the asset management activities of infrastructures like roads, railways, water supply and drainage networks, and electricity and gas distribution networks, the traditional focus is on their geographical location and a network view rather than detailed geometry. For example, when making decisions at the level of a municipality's water supply network, data and digital models must be adjusted to the scale of the physical entity in question. Instead of a 3D geometric representation focused on asset details and geometric accuracy, there is usually a need for a broader view of the system, facilitated, for example, by Geographic Information Systems (GIS). However, if, for example, the purpose of digital twinning is to extract quantities of labour or materials for design and construction phases, geometric detail becomes more relevant, as it will influence the quality of the results. Therefore, there is a need for alignment between the defined purposes for each type of asset and the levels of geometric representation, which may require the same asset to be represented in different ways to meet different uses throughout its life cycle. This technological challenge is already being addressed by the industry, for example, through integrated and interoperable solutions between BIM and GIS models [54; 98].