- combine that data with other sources (elevation data to draw mountains and hills, OpenStreetMap data to add streets and auto-generated buildings...);
- rebuild the scenery using a special tool.
Unfortunately, the rebuild takes a long time (on my machine, it takes about 8/9 hours for a single tile), and the developer running the scenery building infrastructure has left the project - other core developers are in touch with him to recover the data that was stored there in order not to rebuild it from scratch (thus saving a lot of time). Additionally, rebuilding a single tile requires rebuilding at least an entire area, because the scenery elevation at the tile margins needs to match the one of the adjacent tiles, which complicates rebuilds.