Underground development covers a wide range of underground uses, transportation and infrastructures networks; water and energy storage facilities; municipal spaces, housing, business and manufacturing facilities; and overall exploitation of Urban Underground Space (UUS). According to the Greek legal framework on properties underground, transportation networks, such as the metro, are developed deep enough that no compensation is due to surface parcel owners, which are usually a public entity. The current Greek cadastral system is two-dimensional and there are no records for underground transportation networks. As the need for the exploitation of UUS is arising, especially in densely populated Greek cities, such as Athens, the detailed documentation of transportation networks 3D underground property rights is essential. Herein is presented the technical and legal definition of the 3D underground property rights of the Piraeus Metro Station that is constructed in Piraeus Municipality UUS. Three-dimensional underground models for both Piraeus Station and official cadastral parcels are created so as to identify their 3D spatial intersection. For the identification of their legal and spatial status in 2D, the UUS was subdivided into layers in respect to the station’s vertical infrastructure and then correlated to the current cadastral 2D spatial data. The presented 3D underground property rights of Greece’s major urban underground transportation network facilitates its registration in the current 2D Greek cadastral system and contributes to the better understanding and the identification of legal and technical aspects of UUS rights in Greece.

History and the modern world co-exist in Greece’s landscape. The urban spaces of Greek cities contain structures from ancient history alongside contemporary constructions, but intense urban development from the 1960s onwards, as in the historic center of Athens, has led to imbalances with respect to cultural heritage protection. The 1975 Greek Constitution defined the preservation and protection of the cultural environment as a constitutional mandate, and severe restrictions on the exploitation of private properties deemed to be of historical or architectural importance were imposed. Property owners were deprived of their property development rights (DRs), whereas the preservation and conservation of protected constructions became costly, resulting in abandoned buildings and a downgraded urban environment. As the debate over cultural heritage protection and urban regeneration is more topical than ever, the recent legal reintroduction of the transfer of development rights (TDRs) provides new opportunities for property exploitation with respect to cultural heritage protection legislation. Herein is presented a methodological framework on the classification and 3D visualization and representation of DRs and TDRs in relation to the cultural heritage protective framework and its implementation in a selected area of Athens’ historic center. Legal and technical aspects that affect 3D DRs and TDRs are emphasized as key elements in the successful implementation of the TDR process.

Herein is presented a systematic review on property documentation in Greece from 1830 to the present, examining the systems used and their impact on spatial data management and land administration policies. This review reveals that the adoption of the person-based land registry system in 1836, versus the parcel-based Cadastre, led to fragmented property documentation and hindered coherent land administration policies. The establishment of the Hellenic Cadastre in 1995 marked the transition to integrated property documentation within the sole official parcel-based system, facilitating spatial data management and sustainable development. The cadastral survey revealed significant spatial and descriptive fragmentation due to incomplete spatial and legal documentation, unregistered administrative acts, and unregistered public property, which also affects the operational Cadastre. This paper contributes to the literature on the full transition from land registries to a Cadastre, and its impact on spatial data management and overall land administration.

The Hellenic Cadastre, which is expected to be fully operational by the end of 2025, represents a major modernization step in Greece’s technical and legal documentation of property rights as the successor to the country’s land registry system. It will also constitute a land administration system, since it will encompass not only property rights but also restrictions and regulations in the context of RRR. A significant technical but also legal challenge inherent to this system pertains to the resolution of deviations between surfaces calculated prior to 1990 based on older geodetic reference systems and recalculated today using the current Greek Geodetic Reference System, GGRS87. Deviations that arise from geodetic transformations between older and modern projected reference systems are compounded by limitations inherent in historical surveying techniques and in the geodetic infrastructure that was available at the time. To address this issue, we introduce the Local Area Distortion Factor (LADF), a novel metric factor designed to adjust and harmonize property areas across different geodetic systems. This real-world case study offers a practical illustration of the application of LADF, demonstrating its capacity to enhance the precision of cadastral records while preserving interpretability for both experts and non-experts. LADF can also be used to improve land adjustment processes during the implementation of urban plans, property valuation, taxation, and notary acts that are in different reference systems.

The Hellenic Cadastre, which is expected to be fully operational by the end of 2025, represents a major modernisation step in Greece's technical and legal documentation of property rights as the successor to the country's land registries system. It will also constitute a land administration system, since it will encompass not only property rights but also restrictions and regulations in the context of RRR. A significant technical but also legal challenge inherent to this system pertains to the resolution of deviations between surfaces calculated prior to 1990 based on older geodetic reference systems, and recalculated today using the current GGRS87 reference system. Deviations that arise from geodetic transformations between older and modern projected reference systems and are compounded by limitations inherent in historical surveying techniques and in the geodetic infrastructure that was available at the time. To address this issue, we introduce the Local Area Distortion Factor (LADF), a novel metric factor designed to adjust and harmonise property areas across different geodetic systems. This real-world case study offers a practical illustration of the application of LADF, demonstrating its capacity to enhance the precision of cadastral records while preserving interpretability for both experts and non-experts. LADF can also be used to improve land adjustment processes during the implementation of urban plans, property valuation, taxation and notary acts that are in different reference systems.