## 3 Results
### Results of the Literature Assessment
#### 3.1.3 Grey Literature
This national document states that _\"the generation of Cultural Heritage Risk Maps requires the promotion of documentation programmes in the various autonomous regions of Spain, with the aim of geo-referencing all movable and immovable cultural assets, in all categories, along with other assets which, although they might not be classified as such, represent a distinct value in terms of identity, emotion or evocative meaning for a particular community of citizens\"_. When space technologies are explicitly mentioned, GPS is the most cited satellite-based positioning system. However, in some documents, other constellations are also mentioned and described, such as the Russian system GLONASS, the European system Galileo, and the Chinese system BeiDou, as well as the Global Navigation Satellite System (GNSS) and, more generally, navigation (NAV) technologies (see, e.g., the technical recommendation by the Instituto Andaluz del Patrimonio Historico, 2011 and the guidance published by Historic Environment Scotland, 2018) [30; 32]. This evidence would suggest that these technologies are adopted in the practice of heritage documentation. Finally, GIS, georeferencing and, more generally, geo-spatial information are also considered crucial for planning purposes, and for dealing with the pressure due to modern development. For example, in its review of aerial archaeology in Ireland for the Heritage Council [33], [PERSON] (2008) recommends that _\"further development of mapping (rectification, transcription, image enhancement and integration with terrain models) should be encouraged, and a strategy developed for strategic mapping of the results of aerial reconnaissance in areas under pressure of development, especially where subject to Strategic Environmental Assessment (SEA)\"_. Undertaking the GIS-based mapping of existing and new imagery of sites is necessary in particular in the areas under significant pressure of development or other land-use changes. This specification is interesting given that development and land conversion are among the first sources of concern for heritage bodies (see below results). Regarding the second-ranked technology macro-category, i.e., \"Photography\", the analysis of the sub-categories highlights the predominance of \"Aerial photography (17%; Figure 13). This outcome is not surprising given the well-known long-standing tradition of aerial reconnaissance and mapping of archaeological features by archaeologists. This, in turn, explains the reason why aerial photograph collections are nowadays valuable historic resources for users, and, to be stored and accessed effectively, various initiatives for digitalization as geo-spatial information have been launched by heritage institutions in different countries (see above for the evidence of the association between \"Geo-spatial information\" and \"Photography\"). On the contrary, \"Surveying photography\" and documentation from \"Close-range terrestrial photogrammetry\" and \"UAV\" are much less represented in the analyzed Grey literature, both when aggregation is performed by macro-category and when individual sub-categories are detailed (Figures 12 and 13). In the case of \"UAV\", this low representation is explained by the drone technology being relatively new and still being experimented with (mostly by academia and the commercial sector). In addition, it is important to mention that licensing can be an issue for the systemic uptake of drone use, especially in emergency situations. In that reference, it is only since 2019 that there have been some shared instructions at the European level provided by the European Union Aviation Safety Agency (EASA) [34], which can be further refined on a national level. All these factors contribute to the fact that UAVs have not been fully embedded yet in common practice by heritage bodies and organizations. Instead, the low statistics found for \"Surveyingphotography\" and \"Close-range terrestrial photogrammetry\" need to be better contextualized.