| Value | Category | Cases | |
|---|---|---|---|
| 1 | Surface tunnels | 1753 | 
                                    
                                    4.2%
                                 | 
| 2 | French tunnels | 287 | 
                                    
                                    0.7%
                                 | 
| 3 | plastic houses | 10047 | 
                                    
                                    24.3%
                                 | 
| 9 | not stated | 39 | 
                                    
                                    0.1%
                                 | 
| Sysmiss | 29302 |