Clear directory structure

FreeBSD has a clear separation between base operating system and user-added applications, that means everything which does not belong to the base operating system is under /usr/local directory, and the /usr/local directory contains a directory structure that mostly mirrors the structure found in the / or /usr directory.

For example, the application installed from port tree or package command will be located in /usr/local/bin or /usr/local/sbin, corresponding to /bin, /sbin, /usr/bin and /usr/local/sbin; and /etc directory contains configuration files for the base operating system while /usr/local/etc for user-added applications.

References:
A Comparative Introduction to FreeBSD for Linux Users;
Directory Structure;
Ten Things I like About FreeBSD.