When you look at the map, there is also a scale at the bottom labeled "Ellen". Elle ... old measurement that could vary greatly in length. According to Wikipedia since 1858 there has been a legal requirement that one Elle equals 0.56638 m. That seems to fit with the map as well.
Exactly, Dresdner Elle is correct. Subunit is 24 inches, so that should be the second place noted on a case-by-case basis. Very interesting house, yet a bottomless pit that I probably would not have taken on.