## 2 Methodology
### The Creation of the Mobile Application  
The app creation can be summarized in three steps: the database creation of user data and PoI data; the back end with queries or scripts; and the front end that defines access to the scientific contents of the POIs for the users. The application has been developed with the IDE Unity3D, a complete and powerful tool for developing cross-platform applications. The flow of the app is very simple and is divided into three main parts (Figure 3). Initially, the user signs up and logs in. Registration can be accomplished by filling out a questionnaire. Personal information is not required, while some data such as the user's age, sex, and, more important, preferences on a broad spectrum of cultural content are mandatory. These data are used by a machine learning algorithm present in HUSH. The algorithm should work to personalize the experience on the basis of the preferences expressed by the user in the login step. Then, the user is taken to the map section, where the PoIs will be shown. The selection of the PoIs can be conducted according to different options. The first is inclusive of all of them: the map \"shows all the PoIs\" in the database. Figure 3: The three main steps required for using HUSH. From the left to the right: the login, the research of the Pols, and the fruition of the multimedia contents. The geological and floristic/faunistic targets are highlighted with different colors. The second option allows the user to \"find PoIs around you\", and only the PoIs close to the user's position (in a circle with the center corresponding to the visitor's position and a radius of 500 m) are shown. The third option of visualization is for \"finding the PoIs on a guided tour\". This preference guides the visitor along an already prepared route, suggested according to a keyword-based search. The fourth option allows the user to \"search for POIs\"; the user can visualize only the PoIs that meet the selected requirements. The values used for the selection are the categories inserted into the database. The fifth and last option answers the command \"find PoIs with the intelligent search\", where a machine learning algorithm selects only the PoIs matching the preferences of the visitor using a score assigned to each PoI. The rating is given by the multiplication of the percentages of the user preferences with alpha, which is the normalized value of that PoI for the specific label. So, each PoI has a score depending on the user's preferences. The resulting PoIs will be selected and shown on the map. Once the PoIs are selected, the request is sent to the server, a virtual machine running over the IaaS OpenStack of the Department of Physics and Geology of Perugia and of INFN (Istituto Nazionale di Fisica Nucleare--Perugia Section). The request will be processed by some PHP and Python scripts; in particular, the scripts in Python deal with querying the NoSQL MongoDB database. When a PoI has been selected, the user, with the camera present on their mobile device, targets it (Figure 4). The right framing is suggested in the application for each PoI. One of the characteristics of HUSH is that a visitor can interact with the application, sending feedback on their experience. For this reason, before logging out from the app, a visitor can rate a PoI and suggest new PoIs using a specific functionality named \"Scientific reporter\". This tool asks for some information about a potential heritage site in the form of a brief and free description. Photos and images can be uploaded too. The last section is devoted to the commercial activities and to the touristic and didactic events in the areas surrounding  
Figure 4: The acquisition process of points of interest. (**a**) The visitor finds the PoI; (**b**) the visitor opens the command on the app; (**c**) the app identifies the target image; (**d**) the app opens the contents. The images refer to PoI no. 15 in Tables 1 and 2.  
the PoIs. This part of the application has the aim of improving and supporting the local economy.