Would love to see any of your references for the conference. I cannot find any reference to it prior to Sep 2004. Post Sep 2004 articles all either cite Stephen Davies directly or appear to use his article as a basis. I’ve yet to find one that has a name or a date for the alleged conference, which again is evidence that it didn’t happen. I cannot find any independent confirmation that this conference happened.
I have sampled a number of history of urban planning texts and sites, none of which mention an 1898 conference (below).
1. Mel Scott, American City Planning Since 1890, University of California Press, 10 February 1972.
2. John W. Reps, The Making of Urban America. A History of City Planning in the United States. Princeton University Press, 15 June 1992.
3. Jon A. Peterson, The Birth of City Planning in the United States, 1840–1917 (Creating the North American Landscape). Johns Hopkins University Press, 6 August 2003.
4. Susann S. Fainstein, “Urban Planning,” in Encyclopedia Britannica, https://www.britannica.com/topic/urban-planning/The-era-of-industrialization
6. Richard LeGates, Early Urban Planning V 9. Routledge, 11 November 2004.
7. Jon A. Peterson, “The Birth of Organized City Planning in the United States, 1909–1910.” Journal of the American Planning Association, Vol. 75, No. 2, Spring 2009.