Thank you for the detailed answer. I want to go into more detail in the next few days... but I want to quickly ask one thing: 1. How does a surveyor obtain the file? Ring the bell and then say "Good day, I would like to see your file"?
Exactly. You just have to ring the right place, which is of course the building authority - not the neighbor. The building authority checks whether the so-called
legitimate interest exists. In your case, this applies, so the architect and surveyor have full access to the file and not only, as describes, the right to inspect the file, but they receive the relevant plans/information to clarify the matter, also in copy or, if available, digital form, possibly from the architect who planned and applied for the neighbor’s extension.
This is also logically clear - because how should your architect be able to properly plan your construction project if, for example, he had no knowledge of any building encumbrances and/or boundary violations of the neighbors?
2. Do you know any software with which one can quickly draw plans that are reasonably meaningful?
Why? You pay an architect and a surveyor who are managing your construction project and both are equipped with such standardized software. Moreover, both have full access to the original data.
Of course, you can print out, for example, an online cadastral map and add measurements/sketches, but that does not really help without knowing the building file. So no matter how well you would draw it - before I would say anything meaningful about it (here), I would have 20 follow-up questions or would look at it on site myself. The way to your architect or surveyor is much faster, more reliable, and cheaper at this point.
Best regards Dirk Grafe