First of all, terrain description.
Detailed description of all tiles is here: https://freeciv.fandom.com/wiki/Augment ... k:_terrain
We can roughly divide tiles into following categories:
- water tiles - no significant differences from standard freeciv
- Glacier: limited for land units (only Small Land and Infantry can go here)
- Wet tiles - Swamp, Mangroves - land units movement limited, especially for Mangroves (but Coaster ships can go here). Swamp can be irrigated without water source adjacent.
- Rough terrain (Forest, Taiga, Jungle, Hills, Wooded Hills, Mountains, Volcano) - Dirt Road is required to enable standard shield production (without road -1 penalty), Wheeled Units and Big Land can't enter without Paved Road.
Mountains, Volcanoes without any road accessible only for Small Land units (Volcanoes are not generated, they appear as Global Warming effect) - Plain tiles (Plains, Grassland, Tundra, Desert) - road add Trade point, no restriction for land units.
Tribe, Settlers, Workers, Slaves, Migrants, Builders and Engineers can improve terrain, making:
Dirt Road, Irrigation (require Agricultural Farming and adjacent fresh water - if not Swamp or Oasis), Paved Road (Masonry), Railroad (Railroad), Fort (Carpentry), Fortress (Construction), Water lock (Steam Engine), Farmland (Chemical Synthesis), Oil Platform (on Deep Sea, with Offshore Exploration), Wind Turbine (on irrigated Hills, with Environmentalism).
Builders and Engineers can make Airstrip and Buoys (Radio), Airbase (Radar).
Engineers can make Highways (Automobile).