What is a cluster

Michael Porter (1998) defines clusters as a “geographical proximate group of interconnected companies and associated institutions in a particular field, linked by commonalities and externalities”.
Michael Porter is the most popular author in the field of clusters: he has proposed an attractive model  and he has been able to highlight the consistent elements for success. In the early nineties, in his book “Competitive Advantages of Nations” 1990, Porter not only develops a new methodology for analyzing determinants factors of competitiveness of a country, but also he energizes it with a new design of public policies of reinforcement. Someone has called him the Harry Potter of economists. He proposes a “Strategic Management “, considerating a region as a company, from its competitive advantages. M. Porter was invited to Catalonia, and he directed a first study about “The Competitive Advantages of Catalonia” Department of Economics and Finance 1992, Monitor Company /Michael Porter. Since then, the Catalan Government have applied their analysis and an accurate model of help in the development proposals of the industrial sectors of Catalonia.

The definition of a cluster is a group of people or things gathered or growing together.
A bunch of grapes or a bouquet of flowers are examples of a cluster.

Conditions for defining a cluster
Clusters share four critical characteristics:

Proximity: the companies need to be sufficiently close in space to allow any positive spillovers and the sharing of common resources to occur.
Linkages: they need to share a common goal (for example, final market demand) for them to be able to profit from proximity and interaction.
Interactions: being close and working on related issues is not enough. For positive cluster effects to occur, some level of active interaction has to be present.
Critical mass: there needs to be sufficient number of participants present for the interactions to have a meaningful impact on companies’ performance.