I used to live just off what turns out to be the B170, in Belfast. So I've made sure it's mapped from start to end. It starts as the Belmont Road, from the bottom where it meets the Holywood Road, continues up past the roundabout, and up over the Craigantlet Hills, where it becomes the Ballymiscaw Road. Somewhere along that stretch it changes from being in Belfast City Council to Castlereagh: both have the road 'finishing' at that point, so from a purely administrative POV, the "direction" of the road changes at that point. I've reflected this by splitting the road at the closest point to where I can remember the council signs being. If this causes a problem in rendering, someone can always unify things.

(As an aside: we don't seem to have boundary information for the 26 councils in Northern Ireland yet. The plans to replace these with 7 "super councils" seem to have been mostly abandoned, and the current divisions are likely to be in place for at least another 3 years, so it might be worthwhile trying to source this information.)

The route then continues to the end, goes down a portion of Whinney Hill, and then the full length of the Craigantlet Road (which later becomes the Ballysallagh Road) until it meets the A2 Belfast-Bangor road.

Most of the Craigantlet/Ballysallagh Road was missing, so I filled it in, and also added a few of the connecting roads down from it into Newtownards.