skiing is done at a ski hill or resort on snow, grass, ice, etc.
some areas are big and some are small
Skiing and swimming. There are some others but those are the two I'm sure of.
In some areas but others are kinda cold.
they're not.
Click on the 'Powder Skiing' link below for some tips.
Some popular skiing methods include downhill skiing, cross country skiing, moguls and slalom. If you are feeling adventurous, you may consider snowboarding - a version of skiing that utilizes one "board" instead of two separate blades.
From hills to mountains that are cleared of trees. Some skiing is in the trees.
This is a VERY broad question, in some areas it is, in others it is not.
Sanitation issues
cotton grows in places where it is hot or tropical areas. some places are may be too cold.
In some areas, soil might be more fertile then others, or there might be better protection, and also maybe a more significant water source.