## 1 Introduction  
In order to assess indoor air quality (IAQ), low-cost IoT systems are emerging for straightforward and on-time monitoring. Recent advances in the design of IoT technologies for IAQ management can lead us to modern \"cognitive buildings\", very much focused on the users and occupants, and hence contributing to the reduction in human exposure to most indoor pollutants. 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, a harmful indoor air pollutant, setting the focus on the occupant and the occupancy. Indoor air quality (IAQ) stands for the management of three distinct sources of air pollution: physical pollutants related to light, electromagnetic files, air temperature and relative humidity and noise; chemical pollutants, derived from carbon dioxide and carbon monoxide, volatile organic compounds (VOC), and some others, such as ozone, sulfur dioxide, nitrogen dioxide, formaldehyde, ammonia, ozone and radon; and biological pollutants, such as fungi, viruses, bacteria, among other factors [1; 2; 3]. The lack of IAQ leads to the so-called \"sick buildings\" [4], and according to the World Health Organization (WHO) literature on the subject, about 30% of the buildings made in the 1970s and the 1980s are suffering from this kind of syndrome [5]. A few steps in the right direction have been taken since then to prevent \"sick buildings\", with some WHO-specific publications, namely the first edition of the \"Air Quality Guidelines for Europe\", in 1987 [6], followed by the second edition in 2000, including a specific section describing all indoor air pollutants [7]. More recently, in 2005 [8], WHO has updated specific guidelines for IAQ promotion, and in 2009, it published new recommendations concerning public health protection from risks derived from indoor dampness and microbial growth [9]. In 2010, WHO specified the recommended figures for nine of the more frequent indoor air pollutants [10]. From all indoor air pollutants, radon is consensually considered one of the most critical to human health [11], given its radioactivity, which results from the uranium decay available in rocks, soils, and building materials [12; 13; 14]. Since it is considerably heavier than air, radon tends to be trapped indoors mainly in badly ventilated buildings [12; 13; 14]. It is reported that indoor radon concentration is particularly harmful in high energy-efficient buildings, very well insulated and airtight, since the lack of air renovation promotes higher indoor concentration [15; 16]. The modern paradigm of the energy efficiency of buildings, favoring the use of airtight high-insulated windows, super-insulated roofs and facades, and high-performance climatization systems and devices, is leading to the production of ultra-airtight building shells and enclosures [17; 18], disregarding the ventilation need for air renovation and indoor air quality (IAQ) promotion and improvement, either by natural or mechanical means [19; 20; 21]. The exposure to natural radiation associated with indoor radon levels (\({}^{222}\)Rn) has been an object of growing concern, especially since the first studies that correlated the effects of indoor radon with the occurrence of various diseases, including cancer, began to emerge [22; 23; 24; 25]. In fact, in the decades of the 60s and 70s of the 20 th century, several research studies related the exposure to high radon concentrations with lung cancer [26; 27], primarily if related to other factors, such as tobacco consumption [28], or exposure to mineral dust [29], e.g., from the mining activity [30]. The relationship between the granite geological substrate and high indoor radon concentration is a piece of evidence that has been proved by many assessment studies carried out in situ, which also led to active research into the origins of the gas itself, which is strongly related to a specific set of nature granite/schiot lithologies.