In this paper, the relationship between the heat transfer coefficient of dropwise condensation on a vertically flat surface and geometric arrangement of drops in dropwise condensation was quantitatively investigated using geometric parameters (such as the degree, degree distribution, and clustering coefficient) in graph theory. In this regard, the geometric parameters of target drops having radii >= 0.05 mm were evaluated from time-series images of dropwise condensation using the image-processing approach developed independently by the authors. The results indicated that the heat transfer coefficient exhibited a clear correlative relationship with the overall average degree and time-averaged clustering coefficient. (C) 2016 Elsevier Ltd. All rights reserved.