Flood vulnerability assessment is a critical research area due to the increasing frequency and severity of flooding. However, the assessment of vulnerability is a challenge due to its multi-dimensional nature, and hence, a significant number of different criteria must be considered. Thus, the problem is formulated as a multi-expert, multi-criteria decision problem involving fuzziness. This study proposes an integrated approach combining the Interval-Valued Intuitionistic Fuzzy Analytic Hierarchy Process (IVIF-AHP) with geospatial techniques. IVIF sets can better express hesitancy and uncertainty and, more generally, the grey information provided by multiple experts. The methodology was applied to representative river basins in Rhodope, Greece, using 17 indices. Vulnerability indices were transformed into spatial layers, and a weighted overlay technique generated a comprehensive vulnerability map indicating the spatial distribution of flood-prone areas. The results highlight the need for multi-expert involvement due to diverse perspectives, enhancing the understanding of flood vulnerability factors.