Connecting a set of locations with a transport network is commonly a cost-benefit consideration; how much each option costs and what is the related benefit. This is the reason why an area may not be entirely serviced since the additional costs related to expanding a transport network may not justify the marginal benefits. The is notably a challenge for transportation and telecommunication networks in low density (or low income) areas.
The above example considers a set of alternatives to service five locations by a transport route. The revenue potential of each location is indicated (e.g. a function of the population) and becomes effective if that location is connected. A direct link (option A) would create a benefit, but it is worth considering the growing benefits of having a longer route that services more locations (options B and C). However, servicing an additional location (option D) reverse the cost / revenue trend, implying that this location could be discarded, leaving network coverage C as an appropriate solution.