I see it as a choice of lifestyle - a great big city or a smaller, more human size town (which could be too small and therefore parochial).

Or maybe they mean - what is the best choice? big or small? or somewhere between the two?

For me the words are less a problem than the meaning. As written in French, it could be:
- the problem of finding the right size between A and B, and/or
- the problem of choosing one or the other of A and B as target and/or, as you say
- the problem of urban planning for entities of all sizes ranging from A to B.

Without that knowledge I would keep as many words as possible out of it since they are likely to focus on a limited number of possible meanings.

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Note added at 1 hr (2006-12-13 11:48:38 GMT)
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Or maybe simply leave it in French. I hardly think it is essential to understanding your text.

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Note added at 1 hr (2006-12-13 11:52:57 GMT)
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Of course it COULD also be social comment, about failed urban planning in the socially deprived areas (cité) and how that has created a sub-class of urban poor and unemployed with little or no feeling of belonging to the "République" (Métropole, as in l'Hexagone):

"socio-economicall-deprived suburban residential areas and good citizenship"

I do think I'm stretching things a tad, but it's the sort of thought that might cross a French reader's mind.

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Note added at 1 hr (2006-12-13 11:53:40 GMT)
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Insert a Y where you think best fit.

a slightly different tac

The cite in Paris especially is a suburban centre, like some of the architectural nightmare new towns of the southern suburbs. Metropole is more of a real big city, a metropolis, like Paris or Lyon proper, not the suburbs. I think the meaning is that a whole range of different styles of city development is envisaged.

Tricky one. The trouble is we've (English) got some pretty specific words for "cité" and picking any one of them restricts the meaning more than in French. What strikes me is that a "cité" is usually a pretty small area, whether it means an estate, or the "old town" or whatever, and a "métropole" is usually pretty big. So I'm wondering whether you could pick a couple of adjectives to replace the nouns? The above are just suggestions. It was more the approach that I wanted to suggest to you.