on the minimum solution. Clearly the numerical analysis of the shortest path problem is complex and becomes increasingly so when constraints (eg minimum separation distances) are placed the junction locations: the on solution proceeds using Lagrangian multipliers (cf Section 2.5). (b) Centres of unequal size. Once we relax our simplifying assumption of centres of equal size, then we return to the locational situation that intrigued Wellington (see Section 3.2.1). If we glance back at Figure 3.5A it will be clear that the junction location shown there is only optimal if all the centres are of equal size. If centre a was very large in relation to centres b and c, then we would expect the junction to shift towards a, as shown in Figure 3.7.