Undefined lands: A review of their role as an underexplored resource of landscape

Landscape areas have spatial discontinuities, such as vacant land and leftover spaces. Undefined lands present a compelling area for landscape research, aesthetical experience, and development of cities which discuss irregular and unexpected aspects in landscape settings. Having lacked a formal definition of undefined land, this study aims at proposing keywords of undefined lands, a comprehensive review of knowledge, and definition. In order to promote new aspects of such spaces in the future research, the study conducts a systematic analysis of 65 peer-reviewed papers for their temporal trends, locations, methods, key authors, and commonly studied aspects. Results show the production of vacancy and the temporary use of undefined lands as an opportunity, and a flexible method of regeneration. An increase in publications over the past 30 years demonstrates that leftover space is an evolving subject. Although socio-ecological aspects are the most effective, serious gaps are mentioned in the literature considering aesthetical and ecological qualities in leftover spaces formed by visual, sensorial (hearing, touch, smell, taste), and cognitive perception. These gaps in the literature suggest that it is important to understand the potential effects of repurposing citizen's ideas about interventions in which to use leftover spaces. Having identified the knowledge gaps, undefined lands are suggested as a significant sub-discipline in landscape research.