Scale = magnitude, size. Your rewrite is a bit awkward and I think a bit off; I would paraphrase it as: They have forgotten how much exchange of work, merchandise, and ideas can be accomplished in a city, and this (volume of exchange, etc) must be restored .
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CadzaoThe author wrote it in a rather complicated way, so it is so difficult for me to get what he means.which must be restored
Could you tell me what makes you think he seems to be on the positive side of it?
CadzaoI know, but why "which must be restored?" (because of "MUST"?)must be restored because they are valuable