ok, after listening to ideas and suggestions, i come to you with this: again, not finished, so please take that into account. the finished version will look a lot cleaner, and include fancy bits.
the black lines are railway tracks: impassable.
the green areas, - parks: impassable.
the river thames may only be crossed at the bridges.
oxford street may only be passed at oxford circus. (i have placed a little "bridge" at this point).
bonus for each of the red zones, they include buckingham palace, houses of parliament and trafalgar square. i plan to add the london eye, tower of london, plus any other suggestions.
railway stations (in black) bonus for owning them all. there are currently 6, but maybe this is too many.