Different Representations of Distance

Three major representations can be used for distance:

• Euclidean distance. A simple function of a straight line between two locations where distance is expressed in geographical units such as kilometers. Commonly used to provide an approximation of distance, but almost never has a practical use.
• Transport distance. A more complex representation where a set of activities related to circulation, such as loading, unloading and transshipment, are considered. Additional elements such as costs and time are also part of the transport distance. On the above figure, the transport distance between locations a and b includes, pickup, travel by mode 1, transshipment, travel by mode 2 and finally, delivery. The same applies to the circulation of people, although the involved activities will be different. For instance, someone using air travel between two locations will require going to an airport, may transit through an intermediate airport and will finally need to reach his destination from the terminal airport. Transport distance is jointly expressed in geographical units, in cost and in time.
• Logistical distance. A complex representation that encompasses all the tasks required so that a movement between two locations can take place. Logistical distance thus includes flows, but also a set of activities necessary for the management of these flows. For freight movements, among the most significant tasks are order processing, packing, sorting and inventory management. Geographical distance units are less relevant in its assessment, but the factors of costs and time are very significant. Time not only involves the delay related to management and circulation, but also how it is used to service the transport demand, namely the scheduling of pickups and deliveries. On the above figure, the logistical distances between locations a and b, includes an order from b, which is processed, packed and scheduled to by picked up. At the intermediate transshipment location, sorting and warehousing are performed, and finally, at the destination the delivery will be unpacked and used. For the transportation of passengers, logistical distance also concerns a specific array of tasks. Taking again an air travel example, a ticket would first need to be purchased, commonly several weeks in advance. Other common time and cost tasks concern packing, checking in, security checks, boarding and disembarking, picking up luggage and, finally, unpacking. Thus, a three hour flight can in reality be a movement planned several weeks in advance and its full realization can take twice as much time if all the related logistical activities are considered.