Further by Barclay:

But, I must now confess that I wrote a very critical review of the book on this that Tyler praises, Development, Geography, and Economic Theory (1996 in JEBO). I had two complaints. One was that the Dixit-Stiglitz heterogeneous goods model from monopolistic competition is not in fact the main source of agglomeration economies in actual regional economies, although Krugman defended his use of this model in that book by arguing that it was useful for providing a rigorous mathematical model, which it does. He compared himself to the person who provided a map to "darkest Africa" when those who had written of it earlier could only vaguely speak of it in words.

My other criticism, connected to the first, was that there had been a long literature in the 1980s that did mathematically model agglomeration economies (not using Dixit-Stiglitz) that he never cited, in contrast with his citing of the use of Dixit-Stiglitz by others before him in trade theory and by Fujita in urban and regional economics. However, most of this literature was by physicists publishing in regional science or geography journals, such as Peter Allen, who was a student of Ilya Prigogine in Brussels, and Wolfgang Weidlich, who is an associate of Hermann Haken at the Institute for Theoretical Physics in Stuttgart. Krugman has never cited these people, and to be very blunt, I publicly called him out on this when he made a presentation at a session on complexity at the AEA meetings in the early 1990s (he was chairing the session and replied "we can discuss citations later, next question" [end of discussion]). Having made this rather snarky remark, I must admit a hard bottom line: it is very possible that Krugman never actually saw or read any of this literature, and certainly none of these people are as deserving of this prize as he is, due to his broader accomplishments (and if he did read it, he may have rejected their approaches as too "ad hoc," even if mathematical). However, at the time I thought it highly likely he was aware of it, which is what motivated the much more critical remarks I made in my book review, which I shall not repeat here, inappropriate as they would be on this day.