# Multi-Purpose Ontology-Based Visualization of Spatio-Temporal Data: A Case Study on Silk Heritage
## 4 Representation of CH Spatio-Temporal Data. The SILKNOW Case  
In Section 3.2, the general multi-purpose features of STMaps were explained. In this section, we describe the SILKNOW implementation of STMaps, where we focus on CH. In the particular case of the silk-heritage data stored for the SILKNOW project, we need to visualize information about silk-related objects. These objects and their properties are received from the SILKNOW's knowledge graph and are filtered by a search engine, so that the map only shows the objects that the user is interested in. In particular, we are interested in showing the following properties of these objects:  
* Production place;
* Production time;
* Type of object;
* Material;
* Weaving technique. The first two elements represent the spatio-temporal coordinates of the object. The first one is obviously used to place an icon on the map showing that there is an object produced there. The other four properties are mapped, by means of the extension we have created to the VISO ontology, into a ring-based representation (Relation Ring in Table 1) showing information about the relationship between each object and other objects shown in map regarding these four properties (see Figure 5). Each object shown on the map has  
Figure 4: Layered time visualization in STMaps showing data from 17 th–18 th centuries and from the 19 th century. Layered maps always appear in a 3D perspective. Figure 3: Timeline visualization in STMaps showing data from two centuries: 16 th (**a**) and 19 th (**b**). this ring-based representation, and its ring is divided in as many properties as desired. The properties to be shown and their colors are fully configurable. Therefore, by changing the configuration file (stylesheet file), we can change the visual representation, adding or removing elements to the ring and other visualization elements. For this reason, this ring-based representation can be applied outside the SILKNOW context and used with other cultural and non-cultural datasets. As previously said, in the case of SILKNOW, four properties (time, type of object, material and weaving technique) are chosen and specified in the configuration file. Therefore, the ring is divided in four parts (see Figure 5). Each section of the ring is then filled with two colors (one darker and one lighter) of the same hue. The amount of dark color with respect to light color represents a percentage. This percentage can also be seen with a number and indicates the ratio of objects shown in the map (only those visualized, not the whole database) that share this very same property with this object. For instance, let us imagine that a particular object of the database is found in Florence (Firenze), Italy. STMaps will show an icon on Florence and the icon will be encircled by a ring divided in four sections: one orange, one red, one green and one blue. Each colored section of the ring represents a percentage. The dark orange area over the light orange area represents the percentage of objects in the map that share the same weaving technique with the object in Florence. The dark red area over the light red area represents the percentage of objects that share the same material with that object. The dark green area represents the percentage of objects sharing the same type. Finally, the blue-colored section represents the percentage of objects sharing the same production time (with a granularity of one century). Figure 5 shows the ring-based representation. The objects on the map can also be interactively explored. For instance, each object can be clicked in order to see a textual depiction of the ring-based information explained earlier. Once an object is clicked, in addition of seeing the relationship of this object with others in the map, we can also gather more information about it by clicking a plus sign. A new window is shown depicting all the data about this object.