I've completed the boundaries of Heuvelland, Heuvelland is a quite big municipality, it consist out of 8 villages of which all individual boundaries are drawn too.
The drawing of the boundaries itself happened with the help of old Popp maps which fall under PD. But since the biggest part of the boundaries didn't change in the past years, I could still use those maps. I even have drawn some roads with the help of it, roads of which I knew that still existed.
The only problem I had was with the village De Klijte. In the time of the Popp maps, De Klijte was a part of Reningelst. But with the fusion of the 70's, De Klijte became an independent part of Heuvelland, and since Reningels is not a part of Heuvelland but a part of Poperinge, I had to search the boundary between it. But I saw that there was a stream between De Klijte en Reningelst, just at the location where the rough boundaries between those two were. So I took that stream as boundary. I believe it's correct.
If someone can correct the boundaries, please do. But now, nominatim and other search engines will give more correct search results.