Objects that sit over more than one grid cell are now said to occupy ALL of them. (finally). And you can now see which cells (the occupied ones) are excluded from the search domain. As a side effect vehicle path-planning is now working a lot better...visualisation helps.
I finally got around to doing it - this should help demonstrate how vehicle nav is working...and make some nice scientific/planning looking screen captures.
There are actually 2 different resolutions of navigation grid: one for fine tuning (for crowds etc) and one for the big chunky vehicles (the dark lines and light lines, respectively).