A method of designing a fibre optic network for a plurality of premises in a geographic area that has existing infrastructure for one or more utilities in the geographic area, 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 describing connections 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 using said fibre optic network design inputs and said existing infrastructure inputs; and electronically outputting the design outputs characterised by performing optimisation with respect to said fibre optic network design inputs and said existing infrastructure inputs using an optimisation model to optimise geographic locations of said nodes and said arcs in the fibre optic network relative to the existing infrastructure, and wherein said optimisation model comprises a tree optimisation model comprising a plurality of trees, whereby each tree is centred at one of said nodes and comprises one or more of said arcs connected thereto, the optimisation model comprising a linear optimisation function subject to linear and integer constraints, wherein said design outputs comprise output node data relating to optimised geographic locations of said nodes and output arc data relating to optimised use of said arcs in the fibre optic network relative to said existing infrastructure, wherein said existing infrastructure comprises a power network. 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 describing connections 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 using said fibre optic network design inputs and said existing infrastructure inputs; and electronically outputting the design outputs characterised by performing optimisation with respect to said fibre optic network design inputs and said existing infrastructure inputs using an optimisation model to optimise geographic locations of said nodes and said arcs in the fibre optic network relative to the existing infrastructure, and wherein said optimisation model comprises a tree optimisation model comprising a plurality of trees, whereby each tree is centred at one of said nodes and comprises one or more of said arcs connected thereto, the optimisation model comprising a linear optimisation function subject to linear and integer constraints, wherein said design outputs comprise output node data relating to optimised geographic locations of said nodes and output arc data relating to optimised use of said arcs in the fibre optic network relative to said existing infrastructure, wherein said existing infrastructure comprises a power network.