1. Spatial Aspects of the Commons
The commons problem is a resource problem with particular spatial characteristics related to resource domains and rights assignments. Resources can occupy exactly the same area (coincident), overlap (intersecting), or have no relationship to each other (independent).

2. The Commons: Spatial Aspects of Private Resources
Consider a case with two resource users, A and B, and a single resource. Assume that A and B act independent of each other, each user has the right, within her/his domain to utilize the resources. The users’ rights are only executables if their domains of rights correspond to some degree with the domain of the resource.
Case 1: A’s domain of rights is coincident with the resource domain. Thus A may exploit the resource, enjoying all benefits and pay all costs arising from exploitation, while B is excluded.

3. The Commons: Spatial Aspects of Open Access Resources
Case 2: Both A and B are able to exploit the resource, since the resource domain intersects with the rights domains of both parties. The full benefit of any act of exploitation fall to the party undertaking the exploitation, but A and B share at least some of the costs – for example, in terms of atmospheric degradation or future reductions in harvestable wildlife.
Hence, the incentive is for overexploitation the resource. This is the essence of the commons problem and illustrates the spatial mechanism behind the classic example of common grazing lands.

4. The Commons: Spatial Aspects of Fugitive Resources
Case 3: With fugitive resources where movement is unidirectional -- for example, from the rights domain of A to that of B -- the initial user (A) gains all benefits from exploitation, but may not bear any of the costs.
Fluvial pollution is an example: an upstream riparian user (A) gets full benefit from polluting a river but none of the costs which are born by down stream users (B).

5. The Commons: Spatial Aspects of Migratory Resources
Case 4: Waterfowl breeding in domain of A and wintering in the domain of B is analogous to the waterfowl conflicts between USA and Canada.
If waterfowl are harvested by A, fewer move to B’s domain to winter, and so B bears the costs of A’s actions through lower potential harvest numbers, but a corresponding lower number will return to A the following year for breeding. Likewise, if B harvests the waterfowl when they are in B’s domain, a lesser number will be available for A, and corresponding lower number will return to B the following year.