The question of how to order our knowledge is as old as systematic acquisition, circulation, and storage of knowledge. Classification systems are known since ancient times. Web technologies foster self-organized knowledge production and folksonomies are pictured as counter examples to expert-based designed knowledge ordering systems, such as library classifications or domain-specific ontologies. However, a closer look into the structure of user-generated content (e.g., the category system of Wikipedia) and its temporal evolution reveals surprising similarities to more traditional classification systems. In related work we have used evolutionary analysis of the UDC, treating it as a stable reference system over against the volatility of the knowledge landscape represented by the constantly shifting knowledge network in Wikipedia (Akdag Salah et al. 2011; Scharnhorst et al. 2011). We also have used the UDC as a case study in ontogeny to demonstrate the instantiating evolutionary tree of the UDC over time (Akdag Salah et al. 2012), reflecting the socio-cultural knowledge landscape of the 20th century in which it developed. We see KOSs functioning like artificial languages to describe information objects in a controlled way, rather than as hierarchical trees designed to allocate documents. In this manner both the user-generated category system of Wikipedia and stable reference classifications give evidence of gradual evolution of intension over time as lexical content mutates rather than sudden or jarring theoretical shifts in base knowledge. In this talk we feature work done to visualize the evolution of classification systems, to compare them and to develop new interfaces to collections that make use of available metadata, including classifications.