In spatial science and urban applications, “space" is presented by multiple disciplines as a notion referencing our living environment. Space is used as a general term to help understand particular characteristics of the environment. However, the definition and perception of space varies and these variations have to be harmonised. For example, space may have diverse definitions and classification, the same environment may be abstracted/modelled by contradicting notions of space, which can lead to inconsistencies and misunderstandings. In this paper, we seek to investigate and document the state-of-the-art in the research of “space” regarding its definition, classification, modelling and utilization (2D/3D) in spatial sciences and urban applications. We focus on positioning, navigation, building micro-climate and thermal comfort, landscape, urban planning and design, urban heat island, interior design and planning, transportation and intelligent space. We review 147 research papers, technical reports and on-line resources. We compare the presented space concepts with respect to five criteria—classification, boundary, modelling components, use of standards and granularity. The review inventory is intended for both scientists and professionals in the spatial industry, such as companies, national mapping agencies and governments, and aim to provide a reference to better understand and employ the “space” while working across disciplines.

3D modelling of precincts and cities has significantly advanced in the last decades, as we move towards the concept of the Digital Twin. Many 3D city models have been created but a large portion of them neglect representing terrain and buildings accurately. Very often the surface is either considered planar or is not represented. On the other hand, many Digital Terrain Models (DTM) have been created as 2.5D triangular irregular networks (TIN) or grids for different applications such as water management, sign of view or shadow computation, tourism, land planning, telecommunication, military operations and communications. 3D city models need to represent both the 3D objects and terrain in one consistent model, but still many challenges remain. A critical issue when integrating 3D objects and terrain is the identification of the valid intersection between 2.5D terrain and 3D objects. Commonly, 3D objects may partially float over or sink into the terrain; the depth of the underground parts might not be known; or the accuracy of data sets might be different. This paper discusses some of these issues and presents an approach for a consistent 3D reconstruction of LOD1 models on the basis of 3D point clouds, DTM, and 2D footprints of buildings. Such models are largely used for urban planning, city analytics or environmental analysis. The proposed method can be easily extended for higher LODs or BIM models.

Seamless navigation has attracted lots of attention and many methods have been reported in the literature or made available as commercial applications. The process of navigation can be interpreted as a continuous movement of 3D objects from one unoccupied 3D indoor/outdoor space to another. From a technical perspective, a 3D navigation model is one of the critical components that should be available to perform successful navigation. A major approach to build a unified navigation model to support seamless path computation is linking indoor navigation networks to outdoor road/street-based networks. Because of different sources of indoor and outdoor navigation networks, the major approach fails to build up true seamless navigation models. With regards to this, we propose a unified 3D space-based navigation model (U3DSNM). The presented model ensures all types of spaces for navigation (indoor, semi-indoor, semi-outdoor, and outdoor) have the same representation, management methods, and network derivation approach, thereby building up unified navigation networks to support seamless navigation paths planning. The model can be linked to the international standards (data models) that are also based on spaces, such as IndoorGML and the on-going version of CityGML 3.0. Three navigation path planning cases show the feasibility of U3DSNM.