This note explores how data work takes place in a public sector arena. We report on findings from a 3-year research project with a Danish organisation, which, amongst other things, aimed to improve current data practices in the organisation. We make use of the notion of ‘social arenas’ as a lens to understand the complex setting the organisation is situated in. We find that data work in this context takes place among multiple stakeholders and requires cooperation across organisational boundaries. Moreover, changes in data practices in one site changes cooperation among multiple stakeholders in the arena. Additionally, we develop a diagram of this complex setting, which constitutes an analytical tool that supports our understanding of the site (or sites) of intervention where data work is examined. Our study contributes to the field of CSCW by proposing and showing how the notion of sub-arena helps to comprehend the cooperation and interaction within the surprisingly complex public sector and locate the (sub-)arenas and stakeholders affected by a change in how data is provided and used.