Base_directory
(Project Properties window)
*.prj (or .apr)\PROJECT\Base_directory
A base directory pathname enables all sources and build files to be relative to the given directory, if within it or in a subdirectory.
Specifying a base directory also enables the source or build tree to be located in a different location from the project file.
If not set, the directory of the project settings file is used as the default base directory for the project.