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Shouldn’t be too hard for those who know the historic high points of urban design. Answer below the fold.
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Barcelona, of course. At the northeastern end of the Cerda plan, where urban development and modernistic renewal projects abandoned his famous gridded octagons to create superblocks. (Click on Barcelona in the Categories list to the right if you want to see what some of that looks like.)
You can see the whole interactive map here (this segment is from 1977), though it may require some registration.
