The component plane analysis method in conjunction with the SOM method was used to investigate relevance among one group of health subjects. A transaction log from a public health portal was employed for the study. The subjects from a health subject directory in the portal were extracted and the traversal activities among these subjects were analyzed. The focus theme ‘weight control’ was selected and the related subjects to weight control were analyzed in the visual contexts of the subject component planes. The findings of this study can be used to optimize the health subject directories, and understand users' medical information seeking behavior.