PART II CONCEPTS 6 CONCEPTUAL FRAMEWORKS 6.3 BUILDING THE EUROPEAN DIAGONAL Arguably t he most challenging a spect of t he Diagonal is its mega-scale. Despite visions devised by international bodies and academics, decision makers find it difficult to conceive benefits at such a level of abstraction and long range timeframe. Even within a single country, cooperation between cities at the regional scale encounters many difficulties and rivalries. At city-region scale, individual areas may not necessarily reach a consensus about a comprehensive urban development strategy, not least for lack of pertinent governance and institutional support structures. Nevertheless, government s ponsored a nd a cademic c omparative research48 emerged at various spatial scales. The OECD49 addressed the governance and the involvement of the private sector in long term, high risk regional development projects. The EU COMET programme50 dealt with large scale urban development projects through the role of the private sector, relation between national, regional, local levels and local actors, multi-sectoral approaches, and innovative democratic governance.51 ment projects and institutional arrangements,52 and IAURIF's comparative study of innovative development strategies concentrated on large scale projects as spatial instruments to enhance the economic competitiveness of cities and regions.53 Cities in southern Europe participating in these comparative studies confirm the practice of cross-border knowledge creation and sharing within the Diagonal. The Diagonal projects aims to consolidate such cooperation within its network of 'urban diamonds' and between its major constituent city-regions. Facing global competition, a number of European countries initiated research on mega-city regions, large scale development strategies and implementation instruments. In France, the Club Amenagement et Villes discussed regional develop- Diamonds of the European Diagonal 148 The first results of knowledge creation and sharing between Diagonal cities are shown in Building the European Diagonal.54 The City's viewpoints presented by the mayors are corroborated by the Proyecto Ci ties re search o f t he Fu ndacion Metropoli on Lisbon, Madrid, Barcelona, Marseille and Milan. The core of the book presents innovative projects which provide lessons across the Diagonal.They focus on waterfront developments, solutions for the legacy of international events such as world exhibitions, innovation hubs as drivers of the local economy, new institutional approaches t o public policies a nd i nnovative urban design solutions for eco-boulevards, sustainable transportation, and greening of cities.