Units have a base speed speed
which is the ratio of mp to acp.
You can set damaged units to move more slowly.
You can also allow occupants to add to the speed, up to the
speed-max
limit.
You can define wind-affected units by defining speed in each direction (max-speed only, do others proportionally). Would need 4 distinct mp costs plus a formula to relate to wind strength. Wind speed defined as "how far a particle of air moves in a turn". Unit examples include balloons, dirigibles, sailing ships, floating cities.