Metapackage vs Package
A metapackage is a package of packages. It does not contain code or physically contain the other packages. It is just a convenience tool. If a group of packages should be together, that information can be added inside a metapackage. So you can apt install or catkin build only the metapackage’s name and the coherent group of packages will all be built together.
While populating the package.xml, I realized that you should avoid putting only the metapackage name, and put the actual list of packages instead. Else, catkin build throws a warning, for example –
WARNING: package “grid_map_simpletest” should not depend on metapackage “grid_map” but on its packages instead