Conventionally, two major elements of the transport system provide a level of accessibility; nodes and links. The nodes (A), related to transport terminals, and the links (B), related to transport infrastructures, have a gradient-like expression of accessibility that has been considered in location theories since Von Thunen. This gradient can be like concentric circles for nodes and like linear buffers for links. The closer a location is to these elements, the more suitable the accessibility of a site is supposed to be.
Not every economic activity is dependent on a high level of accessibility, so a range of accessibility requirements need to be considered. An activity having a high accessibility requirement is limited in its location to category range 1, while an activity having a low accessibility requirement can consider sites in category range 3 (including ranges 1 and 2). Activities having low accessibility requirements tend to have more locational choices than activities having high accessibility requirements. However, the former are more willing to bid for these sites than the later. Two important trends have challenged this rather simplistic relationship between accessibility and location:
- Improvements in local, regional and international transportation have considerably lessened the friction of distance. This expands the area covered by each category of site accessibility (TrendT1).
- Improvements in production systems have lessened the accessibility requirements of many activities (Trend T2). This means that an activity has more locational choices.