Augmenting navigation systems with landmarks has been posited as a method of improving the effectiveness of the technology and enhancing drivers' engagement with the environment. However, good navigational landmarks are both laborious to collect and difficult to define. This research aimed to devise a game concept, which could be played by passengers in cars, and would collect useful landmark data as a by-product. The paper describes how a virtual graffiti tagging game concept was created and tested during on-road trials with 38 participants. The data collected in the road trials were then validated using a survey, in which 100 respondents assessed the quality of the landmarks collected and their potential for reuse in navigation applications. Players of the game displayed a consensus in choosing where to place their graffiti tags with over 30% of players selecting the same object to tag in 10 of the 12 locations.Furthermore, significant correlation was found between how highly landmarks were rated in the survey and how frequently they were tagged during the game.The research provides evidence that using crowdsourcing games to collect landmarks does not require large numbers of people, or extensive coverage of an area, to produce suitable candidate landmarks for navigation.Keywords: crowdsourcing; graffiti-tagging; games; survey; landmarks; in-vehicle navigation systems Introduction GPS-based in-vehicle navigation systems (IVNS) are popular and widely used in automobiles today, typically existing as factory-fitted units, mobile (nomadic) devices and smartphone applications. Mobile Human Computer Interaction (HCI) research in this area has primarily focused on issues of usability and efficiency, and the effects on navigational effectiveness and driving performance (e.g. Green et al., 1995). Concerns have also been raised regarding the deleterious effects of prolonged use of IVNS, such as geospatial uncertainty and environmental disengagement (Smiley, 2000, Leshed et al., 2008. It has been suggested that utilising landmarks (defined here as, "an object in the landscape, which, by its conspicuousness, serves as a guide in the direction of one's course" (OED, 2015)) to act as navigational cues within IVNS, may ameliorate these problems in addition to enhancing the usability and efficiency of the device (May et al., 2004). Indeed, augmenting IVNS with landmarks is likely to improve navigation and driving performance, increase driver confidence, improve engagement with the environment, promote enhanced spatial learning and reduce reliance on the system (Oliver and Burnett, 2008). Furthermore, the use of landmarks during the routine provision of directions is also consistent with basic human wayfinding strategies (Burnett et al., 2001). There are, however, significant obstacles associated with utilising landmarks as navigational cues within IVNS, notably identifying the most appropriate landmark to use at navigational decision points, and the laborious nature of collecting, describing and maintaining a database of thes...