<p>Globally, there is increasing interest in spatial data to support ocean governance and manage the growing range of marine-based activities within the Blue Economy. Geographic Information Systems (GIS) are contributing significantly to the collection, analysis and visualization of this spatial data for conservation planning and management of marine resources. However, within the politics of knowledge in this domain, Western scientific and technocratic expertise predominates, while the knowledge of small-scale fishers is marginalized. Many fishers face challenges in developing the spatial data increasingly employed in Marine Spatial Planning (MSP). This epistemic hierarchy, shaping the Blue Economy through MSP, necessitates distinctive and deliberative processes of research engagement with small-scale fishers. In this paper, we describe and reflect on the process of developing and applying a participatory GIS (P-GIS) mapping methodology with local fishers in three different resource poor environments in South Africa. Our findings show that P-GIS can be used effectively with diverse groups across different socio-ecological systems with varying degrees of external support. Fishers report that the resulting maps have empowered them to defend their rights and contribute knowledge to various planning and decision-making processes. We highlight the approach to this research and key principles for developing GIS-referenced spatial data with small-scale fishers, ensuring that their unique relational ontologies, cultural values, and knowledge of oceans and coasts are acknowledged, injustices in resource access are captured, and fishers retain ownership of the maps.</p>