iTerm2 vim cannot map alt key

Since Mac OS X uses the option key to insert characters, regular <A-[key]> mappings won't work. Thus :h i_CTRL-V becomes your friend. Your right arrow mapping, for example, can be typed like this:

mapcontrolVoption→<C-w>l

This will result in what looks like:

map ^[f <C-w>l

Note, however, that you can't copy and paste the above, as ^[ is one character in vim, but is here represented with two characters. Most vim users would suggest, however, that you not use the arrow keys for this (or anything). I use map <C-l> <C-w>l (and likewise for h, j, k) instead, as it keeps my hands on the keyboard.

See this answer of mine on a similar question. My advice is to use :h mapleader.