Dear colleagues, I am doing heatmaps to see the degree of thematic specialization of several institutions along time. I can do the heatmaps for some institutions while for others I cannot. In this last case all I get are maps showing clusters of themes and tagged with institutions but not the red stains’ maps. What can be the reason for this? These are the top 20 institutions so I think it is not because they don’t have enough papers. Thank you very much. Oriana