Title: Exploring and promoting green urban spaces in Vienna - can data about public perception help drive change? Authors: Banko, Gebhard, Birli, Barbara; Stickler, Therese, Sturn, Tobias, Wannemacher, Karin, Wildenberg, Martin, Moorthy, Inian Citizen Science has become a vital source for data collection when the spatial and temporal extent of a project makes it too expensive to send experts into the field. However, involving citizens can go further than that – participatory projects focusing on subjective parameters can fill in the gap between local community needs and stakeholder approaches to tackle key social and environmental issues. The Horizon 2020 project, LandSense, is building a modern citizen observatory for Land Use & Land Cover (LULC) monitoring, by engaging citizens to transform current approaches to environmental decision making. Citizen Observatories are community-driven mechanisms to complement existing environmental monitoring systems and can be fostered through mobile and web applications, allowing citizens to play a key role in environmental monitoring. Within this project, the City Oases mobile application, focused on the city of Vienna, has been developed that aims not only to stimulate civic engagement to monitor changes within the urban environment, but also to enable users to drive improvements by providing city planners with information about the public perception of urban spaces. City Oases was launched in March 2019. Where are the best places for a romantic date? Where can you skate? Where is it cool on a hot summer’s day? Open urban spaces can be used in many ways. Pick an activity in the CityOases app and we show the spots where you can do them, including the rating of previous users and pictures from the location. If you visit the spot you can rate it as well based on a few selected subjective criteria. If you know a cool spot that is openly accessible but not marked in our map yet? Just add it with a list of activities and some pictures. Additionally, you can input your perceptions including whether it is noisy, clean or if the infrastructure is attractive. The picture module within the application promotes you to take photos in the four cardinal directions. Users can search for specific activities, visit one of the points indicated on the map and then evaluate this point. Time period of data collection: 19/03/2019 - 10/11/2019 Types of contributors: General Public, Students Number of contributors: 50 Number of observations: 788 Number of photos: 1846 Associated files: City Oases Vienna 2019.csv, City Oases Vienna 2019.geoJSON, City Oases Vienna 2019 Attributes.csv Keywords: Urban; Urban Spaces; Green Spaces; Activities; User perception; crowdsourcing, Citizen Science; Vienna This dataset is licensed under a Creative Commons Attribution 4.0 International. It is attributed to the LandSense Citizen Observatory, Umweltbundesamt (Environment Agency Austria) and the International Institute for Applied Systems Analysis. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no 689812.