Astvitaliy1982, look in the Stock game for examples. In "Data / Terrain / Data" folder are folders E157N022, W158N022, W159N022 and W178N029, that each contain a same-named ZHF file. The SH4 game sees those files, and replaces the BFD data with those four "tiles" of terrain data. Hence, as Jeff-Groves mentions, you only need properly built data in a proper folder structure for the altered segments you make. The game does the rest of the BFD structure itself. The ZHF files are only 6kb each.
