why roscd changes to install directory in colcon build?

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I used to use caktin_make to build my ROS pakcage, and after catkin_make, when i use command roscd package_name, and it changes to packge location under src directory. Recently i change catkin_make to colcon build, i found that roscd changes toinstall directory after colcon build, so i am confused. i have two question:

1. why in colcon build, roscd changes to install directory? i think this mechanism brings a lot of inconvenience, for example, when i have some config file in package directory, i have to install all these config files to install directory, and may make mistake of the relative path of config file.
2. how does roscd work? how does it found the package location?

i use kinetic ros