= a*(smooth surfaces + efficient hypotenuses)
c*(drunk pedestrians + slippery tramtracks)
d*(long fast downhills / steep sweaty uphills)
e*(taxis + cops + beer can-throwing SUV drivers + holier-than-thou vehicular cyclists)^2
f*(people to admire your style / avoiding that cafe where the cute waitress saw you fall off that time)
h*(Red lights + puddles)
BONUS TIP: If maths is not your thing: Optimal route-finding is a personal expression of the discourse between the cultural, politico-infrastructural and the physical. Discuss.