I'm trying to plan my new garden, and want to sketch it professionally - with dimensions of every element in it.
Is there an Ubuntu program for sketching house plans with vectorial elements, like those in the picture above?
I suggest SweetHome3D, it is in the apt repos. Here is a screenshot, from its website:
It is also on Flatpak. After installing it you can install SH3D to your user with
flatpak --user install flathub com.sweethome3d.Sweethome3d
There is a program called Librecad that may be what you are looking for.
To install LibreCad click the icon above or copy and paste the following command into Terminal
sudo apt-get install librecad
Then Press Enter, enter your password when prompted.