## 1 Introduction  
In 2001, virtually one billion people lived in urban slums. In 2030 the global number of slum dwellers is expected to increase to about 2 billion, if no significant changes are taking place [1]. The worldwide doxology of city life detracts from the shady side of the urbanization process. Asia dominates the global picture of this shady side with 60 per cent of the world's total slum dwellers [1]. _Megacities_, with populations in excess of 8 million, and _hypercities_, with more than 20 million inhabitants [2], are contemporary epicenters of urban poverty. The urban poor in such megacities are mainly living in informal settlements or _slums_.  
Slums are vast, challenging and fascinating urban worlds, but almost fully eschewed by the architectural design disciplines - definitely \"landscape architecture\" is a foreign word there [3]. The common avoidance of slum areas is understandable. Anyhow, the sheer number of slum dwellers and their unacceptable living conditions are an unmistakable indication of the importance of urban slums as a work task for designers. Slum upgrading initiatives only can be successful, if they are entrenched in the participation of the resident dwellers and the engagement of groups of volunteers, in conjunction with intensive links to the local government and administration. Sensitive slum upgrading is an interminable, dusty and malodorous working field. It means \"dirty work\" [4], \"sweat equity\" [5] for dwellers and volunteers, embedded in a cross fire of bottom-up activities and building stones, instead of top-down master plans and pre-establishments. Grassroots engagement is predicated on big numbers of people, but as a rule it faces small or diminutive budgets. In terms of design efforts, expensive and sophisticated methods and tools have to be replaced by pragmatic, simple and effective instruments that allow basic fieldwork and _in situ_ design.  
Slum areas are the most unsurveyed and thus most untraceable parts of megacities. Although some dwellers have access to the Internet (e.g., at _Internet cafes_ or even mobile Internet), their informal settlements frequently appear as blank spots -- unmapped areas and neglected space on official maps and planning materials. As a form of illegal land use, slums are blinded out from the radar of planners and public or commercial cartography, e.g., online maps. Accordingly, Google _Streetview_ and _Teleatlas_ forgo the areas where the poor live. The majority of urban slums shows no street names and no formal addresses [3]. No wonder that informal settlers extensively live in non-consideration. For example _Kibera_, Kenya, one of Africa's largest slums, was depicted as wild forest on official maps, and deemed illegal and ignored by the government for decades [6]. Since 2009 the _Map Kibera_ project has successfully engaged and trained local youth to map their marginalized community, e.g., by using GPS devices and _OpenStreetMap_ (OSM), the collaborative, open source project to create a free editable map of the world [7]. This project put Kibera on the world map and is currently trying to use the geographical data to improve the delivery of services and the implementation of projects. Community members have been enabled to become both most important consumers and creators of information resources [6].