ONLY 'Civ2:Test of Time' supports the additional terrain flag that, when checked (i.e. 'Yes' instead of 'No'), prevents all units from entering that terrain--regardless of Roads.
ToT also supports an 'override impassable' unit flag (in the 'Advanced Unit Abilities section at the bottom of Rules.txt) that when checked for a specific unit, will allow that unit to enter squares with impassable terrain. (NOTE: Air units ignore impassable terrain by default --are unaffected either way.)
The closest equivilant in any other version of Civ2 (all versions are the same in this respect) that I can think of is to change the domain of units with 'Settle' role (5?) to 'Air' (1) and give them limited fuel/range so that if they travel too far from the city they will run out of 'fuel.' The only problem with doing this is that the human player can 'cheat' by giving the Settler a build order (e.g. Irrigate) before the last available MP and the Settler's MPs will be reset next turn (not sure about range). This means that you can exploit this by moving as far as you like just as long as you keep setting the unit to build at the end of each turn. It will give you an unfair advantage when playing against the AI which will only do this by fluke and be pointless when playing against a human opponent (unless you use a 'house rule,' but then you could use the sam erule without changing anything).
(Kind of stupid but then many things in Civ2 are --like the abiilty to sentry land units with Coastal flag at sea without them being lost.)
The problem with what you mentioned about building immobile air units would prevent ALL unit types from entering those squares is that it would defeat the purpose of just limiting Settlers.
Aside from that, I can't think of any other way.
ToT also supports an 'override impassable' unit flag (in the 'Advanced Unit Abilities section at the bottom of Rules.txt) that when checked for a specific unit, will allow that unit to enter squares with impassable terrain. (NOTE: Air units ignore impassable terrain by default --are unaffected either way.)
The closest equivilant in any other version of Civ2 (all versions are the same in this respect) that I can think of is to change the domain of units with 'Settle' role (5?) to 'Air' (1) and give them limited fuel/range so that if they travel too far from the city they will run out of 'fuel.' The only problem with doing this is that the human player can 'cheat' by giving the Settler a build order (e.g. Irrigate) before the last available MP and the Settler's MPs will be reset next turn (not sure about range). This means that you can exploit this by moving as far as you like just as long as you keep setting the unit to build at the end of each turn. It will give you an unfair advantage when playing against the AI which will only do this by fluke and be pointless when playing against a human opponent (unless you use a 'house rule,' but then you could use the sam erule without changing anything).
(Kind of stupid but then many things in Civ2 are --like the abiilty to sentry land units with Coastal flag at sea without them being lost.)
The problem with what you mentioned about building immobile air units would prevent ALL unit types from entering those squares is that it would defeat the purpose of just limiting Settlers.
Aside from that, I can't think of any other way.
please reply soon. (im making a multi-player game based on a volcano filled planet...i need to make some lava creatures!)
