## 1 Introduction
Therefore, to infer indoor radon potential, the knowledge of the geological substrate of the place where the buildings are located is mandatory [31; 32]. Based on the evidence, indoor radon assessment in buildings with foundations on susceptible types of soils became a widespread procedure, especially after the establishment of maximum admissible doses in the Directive 2013/59/Euratom. This directive focuses on reference values that are currently being transposed into legislation in force in several EU nations and thus pushing the citizen towards an increased radon-related literacy, and thus paving the way towardscitizen science, i.e., the science that focuses on public participation, as well as broadening the scientific awareness of the public [33; 34]. This need led to the organization of the data collected in a dispersed way and to carry out national campaigns to draw up radon maps. These maps, however, have suffered from several constraints, namely the long periods required for their execution, since the methodologies used for data collection are highly time consuming and costly, especially when they resort to the use of passive detectors, which require long measurement periods inside the buildings and a period of laboratory preparation to obtain the results. Thus, the use of other methodologies that allow a more expeditious assessment of the radon exposure and the potential for the occurrence of radon in concentrations that may be contraindicated for the users of the indoor spaces is an urgent need. This time, for example, using indirect and comparative methods, in which a relationship is established between other forms of radiation, such as \(\beta\) or \(\gamma\), with the \(\alpha\) radiation released in the radon decay process can be a possibility. This was the case presented and developed by the MARNA project, launched in Spain, and which, according to [PERSON] and [PERSON] (1997), seeks to draw up a highly detailed natural radiation map for the whole Spanish territory [35], and has been developed within the framework of the agreement established between the Spanish Nuclear Safety Council (CSN) and ENUSA. With the results obtained and with the elaboration of the natural gamma radiation maps, [PERSON] et al. (2004) presented a relationship between gamma radiation and indoor radon levels in Spain [36], and more recently, [PERSON] et al. (2017) presented the Spanish experience on the design of radon surveys based on the use of geogenic information [37], which follows on the previous work by [PERSON] and [PERSON] (2014) who based the Spanish indoor radon mapping strategy also on natural radiation maps [38], whose use was justified for the development of a more expeditious tool to assess the level of radon exposure. This approach can be used as a decision support tool, preferably in the pre-construction design phase, for the adoption of passive mitigation measures, or in the case of already built assets, which guide to carry out an assessment analysis that confirms or rules out the need to implement active mitigation measures to minimize the radon exposure to occupants. Thus, this article presents a straightforward preliminary methodology based on the use of natural gamma radiation as an approach for assessing indoor radon potential. This approach correlates gamma radiation to probable radon occurrences, insofar as radiometric surveys to quantify the natural gamma radiation have been carried out to a large extent all over the world, mainly in uranium mineral prospecting campaigns, being, therefore, available and with coverage on a national scale, or, in the case of large countries, on a regional scale. Based on that, the objective of this research is to present a methodology supporting the development of a WebGIS platform, which allows a first approximation to assess indoor radon exposure, placing the focus on the building occupant. The graphical approach enabled by the WebGis platform makes indoor radon potential assessment for a specific building location easy to be visualized by all interested citizens.