Chemical space, sometimes referred to in the literature as the "chemical universe" [69] and recently extended to "chemical multiverse", is a concept that is central and distinctive of chemoinformatics as an independent theoretical discipline. Chemical space refers to all possible molecules as well as multi-dimensional conceptual spaces representing their structural and functional properties, depending on the type of representation. Indeed, in contrast to cosmic space, the chemical space is relative to the structural and functional properties used to construct or define a given chemical space. Since there is not a molecular representation that captures all structural and functional properties, the concept of "chemical universe" has been introduced to account for the alternative chemical spaces of a compound data set that can be generated by different sets of descriptors. Structural representation is the most relevant feature in basically any chemoinformatics application, and computational study and it is an area under constant research. In virtual screening, defining the chemical space to be explored is crucial, as it defines the applicability domain that will be searched. In practice, it is common to conduct virtual screening campaigns focused on regions of the medicinally relevant chemical space. Nonetheless, it is becoming a regular practice to explore novel regions of the chemical space, given by the emerging large-and ultra-large chemical libraries. The chemical space concept has practical applications in many areas of chemistry including drug discovery, organic synthesis, food chemistry, and material sciences to name a few examples. A key distinction between the different ways of mapping compound data sets into the chemical space lies in the type of descriptors that are used to represent the compounds of interest. For instance, the nature of the descriptors employed to represent small organic molecules will be different to describe chemicals with applications in, for example, material sciences. In some cases, the chemical space concept is used to guide drug discovery projects, but a generalized or unique manner to represent visually the chemical space remains elusive. A typical example of this challenge is the visual representation of the chemical space of metal-containing compounds. In drug discovery, chemical space was used as a spatial navigation framework, helpful for understanding and generating knowledge of pharmacokinetic properties and molecular diversity of biologically relevant compounds . As the number of compounds and their information in chemical databases increased, more sophisticated molecular descriptors and visualization techniques were developed to expand their applications.