Effective urban planning, and urban green space management in particular, require proper data on urban green spaces. The potential of urban green spaces to provide benefits to urban inhabitants (ecosystem services) depends on whether they are managed as a comprehensive system of urban green infrastructure, or as isolated islands falling under the responsibility of different stakeholders. Meanwhile, different urban green space datasets are based on different definitions, data sources, sampling techniques, time periods and scales, which poses important challenges to urban green infrastructure planning, management and research. Using the case study of Lodz, the third largest city in Poland, and an additional analysis of 17 other Polish cities, we compare data from five publicly available sources: 1) public statistics, 2) the national land surveying agency, 3) satellite imagery (Landsat data), 4) the Urban Atlas, 5) the Open Street Map. The results reveal large differences in the total amount of urban green spaces in the cities as depicted in different datasets. In Lodz, the narrowly interpreted public statistics data, which are aspatial, suggest that green spaces account for only 12.8% of city area, while the most comprehensive dataset from the national land surveying agency reveals the figure of 61.2%. The former dataset, which excludes many types of green spaces (such as arable land, private and informal green spaces), is still the most commonly used. The analysis of the 17 other cities confirms the same pattern. This results in broader institutional failures related to urban green infrastructure planning, management, and research, including a lack of awareness of green space needs (e.g. connectivity) and benefits (ecosystem services), and the related political disregard for urban green spaces. Our comparison suggests that a better understanding of green space data sources is necessary in urban planning, and especially when planning urban green infrastructure.

Introduction

Urban green spaces have already been the subject of extensive research, largely meant to support green space planning and management (e.g., Hansen et al., 2015; Kabisch, 2015; Rall et al., 2015). However, many of the relevant discussions, and especially formal planning documents, tend to overlook some green space types and overemphasize some others. This is related to the fact that the definitions and classifications available to date seem not to have ended the debates on what is an urban green space, and how the different green space types and categories are related to each other (Cvejić et al., 2015; Taylor and Hochuli, 2017). To make things even more complicated, different green spaces are managed by different stakeholders (public vs. non-public, city vs. districts), and they are characterized by different degrees of accessibility by the public, and many other different administrative features (Kabisch et al., 2016). Formal planning documents in cities often focus on the formal and most broadly recognized flagship categories of urban green spaces, such as parks, forests, allotment gardens, cemeteries, and street greenery. These green spaces have also been the focus of much research because they are clearly demarcated and depicted in reliable, official inventory databases (Feltynowski, 2015; Schipperijn et al., 2010). This is mainly because these green spaces are primarily managed by formal institutions and they are located on public land. Meanwhile, many forms of urban green spaces elude formal classifications, either because they are located on private land or they are not perceived as green spaces through the dominant lens of recreational potential (e.g., arable land or urban brownfields), or because of their small spatial scale, temporal and transitory character as interim or brownfield sites, as well as the uncertainty of land tenure and changing governance settings. Such informal green spaces have been defined by Rupprecht and Byrne (2014) as those covered with vegetation, usually neither designated nor recognized by governing institutions or owners as spaces for use by the inhabitants.