Meaning of the underlined part

Meaning of the underlined part

The passage below is from The Library: A Fragile History by Andrew Pettegree.

The Dunfermline design reflected the somewhat experimental character of Carnegie’s vision of the public library. By 1904, it was already too small and had to be remodelled and expanded. A children’s library was substituted for the ladies’ reading room (women, on the whole, tended to prefer the general reading room), and the space previously allocated to the librarian’s flat was incorporated into the floor plan. The library still thrives, thanks in part to a recent extension capitalising on the library’s magnificent position overlooking the cathedral, while preserving the historic core of Carnegie’s building. Carnegie would give another forty libraries to his native Scotland, including five in Dundee, and £250,000 for a free public library in Edinburgh. Equally generous provision for England, including a whole branch network for Birmingham and Manchester and libraries in many county towns, would bring the total of Carnegie libraries in Britain and Ireland to 660.

The underlined sentence is about remodeling of Dunfermline library.

The ladies’ reading room is replaced with a children’s library.

Right.

But... the part after ‘and’ I cannot visualize.

I don’t know what ‘librarian’s flat’ means, but ‘flat’ seems to mean ‘a flat surface’ or ‘a flat space’. (Am I right?)

And the meaning of ‘floor plan’ by dictionary says ‘a technical drawing to scale, showing a view from above’.

But these two meanings don’t incorporate into any sense. How can a real space (librarian’s flat) be incorporate into ‘floor plan’?

Or,

Does the underlined part say they just do away with librarian’s flat (since librarian can do their job without their exclusive room)?

Thanks in advance.