The palette
Water does most of the drawing here, and it takes a single ink for all of it: the bay, the lakes and the cuts between them. Choose a blue deep enough to hold its own beside the dense downtown streets, so that the chain across the top stays readable down to its narrowest passage. Green comes in strips rather than masses, the arboretum and a few wooded slopes; a soft tint is enough. The meeting of the grids needs no colour of its own, only a street line fine enough for the change of direction to show.