Representation of a Movement as a Spatial Interaction
Movements involve three basic categories: freight, people
and information. Representing a movement as a spatial interaction involves
- Locations. A movement is occurring between a location
of origin and a location of destination. i generally
denotes an origin while j is a destination. The representation
of origins and destinations commonly involves centroids.
is an abstraction of the attributes of a zone at a point. This
is of particular relevance when the attributes of the movements
considered are zonal (e.g. ZIP codes, cities, states, etc.) while
the graphic representation of these movements requires specific
origins and destinations. For instance, showing flows between ZIP
codes would implicitly require the generation of one centroid
for each ZIP code.
- Flows. Flows are generally expressed by a valued vector
Tij, representing an interaction between locations
i and j.
- Vectors. On the above figure, two areas, zone i and zone
j, are represented as two centroids, i and j. A
vector Tij links two centroids and has a value
assigned to it (50) which can represents movements such as tons
of freight, numbers of passengers per day, or number of phone