Alejandra Rodríguez Sánchez Alejandra Rodríguez Sánchez University of Krems Press 2025 Key points • Irregular migrants, like all people, leave behind data traces – through surveys to digital activity and use of public services. These traces can indirectly signal their presence, even when their legal status remains unknown or unrecorded. • This chapter explores how metadata and alternative data sources, such as social media, mobility records, and mortality registers can complement traditional statistics and offer new ways to estimate irregular migration. • Pilot studies from the MIrreM project show that while these approaches are limited and ethically complex, they can be adapted and combined to improve understanding of irregular migrants, including their presence, behaviours and needs. PDFDocument eng 2025-09-30T07:41:33.119818Z 2025-09-30 Data traces Metadata Digital footprints Indirect measurement Visibility 553186 b application/pdf http://creativecommons.org/licenses/by-nc/4.0/