landclass files (*.bgl) define the type of autogen scenery that is drawn, like forest, desert, city, suburb, etc.

As they dont contain scenery objects of their own, rather just tell autogen what to draw, they are small files.

I use a utility called Landclass Assistant (John Cillis-at Avsim) to modify landclass, generally to place towns, cities, etc. (even golf courses   ), in areas neglected by FS.

A good upgrade to the autogen scenery in those areas that FS overlooked.

Cheers,
Dave