In communication, the notion of medium refers to the means by which a message is transmitted between a sender and receiver. It is the communication channel. Public space can be considered a medium as it communicates the meaning or message of a work, and also because it has a recognisable influence on what is seen and makes a contribution to the work.
The medium can play a more or less predominant role in the project. An artist can choose a location for its geometric and practical qualities, and remain indifferent to the other aspects of the space, which is referred to as a “support medium” (backdrop).
The artist may also choose to use elements of the space as raw materials for the work, which is referred to as a “material medium”.