Vim: how to enter insert-anywhere/canvas mode?

Question

How can you put vim in an insert mode where the entire screen is effectively whitespace i.e. you can type anywhere?

I know it's possible, I just cannot remember the command, unfortunately!

This allows you to draw diagrams and whatnot easily, I hope this rings a bell?

---

Update: Thanks to @phd I made:

                                                    ┏━━━[ Tasker Radars ]━━━┓
                                                    ┃ 🔴 has 1 mile radius  ┃
                  ,,ggddY''''Ybbgg,,                ┃ 🔵 has 5 mile radius  ┃
             ,agd'''              `''bg,            ┃ 🌕 has 20 mile radius ┃
          ,gdP'                       'Ybg,         ┗━━━━━━━━━━━━━━━━━━━━━━━┛
        ,dP'                             'Yb,
      ,dP'         _,,ddP'''Ybb,,_         'Yb,<━━━━━━ 20 miles
     ,8'         ,dP''         `'Yb,         '8,
    ,8'        ,d'                 'b,<━━━━━━━━━━━━━━━ 5 miles
   ,8'        d'                     'b        `8,
   d'        d'        ,gPPRg,<━━━━━━━━━━━━━━━━━━━━━━━ 1 mile
   8         8        dP'   `Yb        8         8
   8         8        8)     (8    🔴  8    🔵   8    🌕
   8         8        Yb  🔴 dP        8         8
   8         Y,        '8ggg8'        ,P         8
   Y,         Ya                     aP         ,P
   `8,         'Ya        🔵       aP'         ,8'
    `8,          'Yb,_         _,dP'          ,8'
     `8a           `''YbbgggddP'''           a8'
      `Yba                                 adP'
        'Yba              🌕             adY'
          `'Yba,                     ,adP''
             `'Y8ba,             ,ad8P''
                  ``''YYbaaadPP''''

Answer 1

Set virtualedit option:

set virtualedit=insert

http://vimdoc.sourceforge.net/htmldoc/options.html#%27virtualedit%27