There is a General Motors Building in both New York City and Detroit. Or at least their once were buildings of the same name in both cities but then GM moved into the Renaissance Center on the Detroit River and the original General Motors Building was renamed Cadillac Place. OF course in 1946, the year of this book, the GM Executive Offices were in 1775 Broadway, now 3 Columbus Circle.
The point is that General Motors had a strong presence in both cities. Detroit was the industrial hub, the home of operations. New York was the financial center, the place where the company raised funds and dealt with the corporate world. The separation mirrored the corporate structure of GM, though the physical locations don’t perfectly map onto the company structure. By 1946, GM had 30 divisions and each was almost a complete company. The corporate office provided certain central services – legal, financing, etc. – that held the group together.