The way I treated this on Linux is that /usr is packages installed by the package manager and /usr/local is where ad-hoc compiled (./configure && make install)

The way I treated this on Linux is that /usr is packages installed by the package manager and /usr/local is where ad-hoc compiled (./configure && make install) software goes. I always assumed this from --prefix=/usr/local being the default in autotools. From wikipedia: (Historically and strictly according to the standard, /usr/local is for data that must be stored on the local host (as opposed to /usr, which may be mounted across a network). Most of the time /usr/local is used for installing software/data that are not part of the standard operating system distribution (in such case, /usr would only contain software/data that are part of the standard operating system distribution). It is possible that the FHS standard may in the future be changed to reflect this de facto convention.)