As far as I know, tracing an outline of the windmill itself, as long as you aren't copying the entire picture, and as long as you aren't planning to sell your map or list it as an original drawing... I don't think that violates copyright law. If I remember correctly if you have changed more than 50% of the original, it doesn't meet infringement laws.
Realize though, my knowledge of infringement laws are literary based, not visual art based. That being said, windmills are 'fairly' universal objects. Meaning there isn't a lot of difference from one to another. The basic design is the same.