This is a simple example level. You can try it by placing the 
files somewhere under the wings2/levels -directory. You can 
also pack it to a .lev file by using the Makelev program 
on ground.xml. 

The idea is that the level consist of a data map, which defines
terrain types (see data_colors.png for reference), visual map,
which defines what the level looks like, and optionally one or
more background layers. 
