This route is a good starter for a few hours out on the bike. If you are riding there from Edinburgh, you can start above Currie/Balerno to the east of Harlaw. I normally do it clockwise, and most of it is reasonable in the wet.
Avoid the path you can see on that map which goes along the north side of Black Hill, as it is boggy when wet.
If doing it clockwise, the part of the route at the west of the map which goes down a road lined with trees just before it crosses the reservoir has some singletrack either side of the road, so you aren’t wasting a descent on the tarmac.