Overview of volumes of Trap Danmark with links to digitized volumes.
Topography 1828: https://play.google.com/store/books/details?id=w6BeAAAAcAAJ&rdid=book-w6BeAAAAcAAJ&rdot=1
Link to Trap Danmark: Sonderburg, Tonder, Haderslev, Aabenraa Amts: Trap Denmark. Vol. 9 [fifth edition].
Trap: http://runeberg.org/trap/
Lexikon of places: http://www.graenseforeningen.dk/leksikon/b/all/4203