The best I could find is that there are 3 cartographers listed for the maps in FR campaign setting 3rd edition - Dennis Kauth [RIP], Rob Lazzaretti [map lead at the time] and Todd Gamble [quoted as saying that Rob taught him]. I would assume it was Rob Lazzaretti who did that map, as the lead carto at TSR/Wizards at the time. It doesn't fit kauth's style and Gamble was newer. Maybe collaborative, who can say. I would assume that Wizards either sought Schley out for having a similar style, or more likely asked him to produce in a similar style. And then he just took it further and better.
From what I can tell Mike does not come around much but obviously he could tell you.