INVISIBLE CITIES XXVIII -- Cities and Signs: OLIVIA

London

OLIVIA: It makes sense that Olivia, the city, is a wealthy city, as olives are historically a symbol, not mention evidence, of wealth.

The opening sentence continues to emphasize the deconstrivist motif of the entire book (and, again, such an Umberto-Eco, at least as far as this blog is concerned, kind of motif it is), that words [or signs] and the things they represent are not necessarily the same thing--they occupy different spaces--though, as Polo tells the emperor, there is a connection between the two.

1. Is there a theme or plot-device (as it were) tying together each of the chapters?  If so, what's going on in chapter 4?
2. Does Olivia exist?
3. "If there really were an Olivia of mullioned windows and peacocks, ... it would be a wretched, black, fly-ridden hole....": why?  The literalist in me wants to say that, well, there must be a natural hierarchy supporting any wealthy city, that below the luscious green apex with its mansions and gold filigree and white peacocks, must be churning away a massive mechanism of industry with all its accompanying soot and slag.  I don't know if this is what Calvino's getting at.  Is he being less literal, more figurative?
4. And I just can't wrap my brain around the last sentence.  The abstraction is too much for me.  What do you make of it?