1. A method of designing a fibre optic network for a plurality of premises in a geographic area that has existing infrastructure, the method comprising: electronically receiving fibre optic network design inputs comprising data indicative of a plurality of nodes in the fibre optic network and data indicative of arcs extending between said nodes in the fibre optic network based on allocated bandwidth for said premises in the geographic area; electronically receiving existing infrastructure design inputs comprising data indicative of said existing infrastructure that can be used as geographic locations for said nodes and said arcs in the fibre optic network; electronically generating design outputs by optimising geographic locations of said nodes and said arcs in the fibre optic network using said fibre optic network design inputs and said existing infrastructure inputs and using an optimisation model comprising a linear optimisation function subject to linear and integer constraints, wherein said design outputs comprise the optimised geographic locations of said nodes and said arcs in the fibre optic network relative to said existing infrastructure; and electronically outputting the design outputs, wherein said existing infrastructure comprises a power network and said optimised geographic locations of said nodes comprises a plurality of power poles of the power network so that at least one fibre optic cable can be hung therebetween.