The term is borrowed from Thomas Sieverts, Zwischenstadt, zwischen Ort und Welt, Raum und Zeit, Stadt und Land (1997), which questioned the somewhat old-fashioned idea of the European city as a network of dense, historical city centres and rural landscapes and instead included more recent phenomena: infrastructures, peri-urban extensions with undefined borders, etc.

Lyon’s municipal councillors made several trips to Barcelona in the early days, which partly led Henri Chabert, the councillor for urban policy, to create a ‘public space’ service in the municipality and appoint several experts as advisers (Jean-Pierre Charbonneau, Gilles Clément).

See Adolf Sotoca and Oscar Carracedo, Naturban, Barcelona’s Natural Park: Rediscovered Relation (Collegi d’Arquitectes de Catalunya Publishers, Ajuntament de Barcelona, 2015).

In Boston, between 1878 and 1894, Olmsted created a continuous green system known as the Emerald Necklace. Starting with a historical legacy of the common, he proposed an urban extension along the bank of the Charles River, followed by the improvement of the Muddy River, and the landscaping of several adjacent green areas, finally merging with Franklin Park.

One example among others is the Swiss Confederation’s revision of the ‘Federal Act on Spatial Planning’ in 2014 to drastically reduce the possibility of new urban extensions. In the same decade, the French government promoted several initiatives that made any urban extension more difficult.