Traditional network location theory is concerned with the optimal location of facilities which can be considered as single points (emergency medical service stations, switching centers in communication networks, bus stops, mail boxes, etc.) However, in many real problems the facility to be located is too large to be modeled as a point. Examples of such problems include the location of pipelines and high speed train lines, the design of emergency routes, newspaper delivery routes, subway lines, etc. We will refer to this kind of facilities as extensive facilities or structures, and they may have the shape of a path, a tree, a cycle or a more general subgraph.
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