I tend to map before rather than after, although my planning is rather loose, with cross sections and rough schematics done from memory rather than measured. I often find though that when I actually do measure I have to change my ideas a bit. For example in my new 'zone one' kitchen garden my plans evolved....
This was my first design:
with keyholes along a central path...
When I actually measured it, I found the area was much more square than I thought, so I came up with this design...
with perennials on one side and a semicircular annual garden on the other.
When I came to make the beds I felt that six beds would end up rather small, so I made four:
I'm thinking now I may make a roundish bed in the centre to avoid the sharp corners...still evolving!
I think doing a plan of my whole area would be too much work now - I did have an overall scheme before I started, and again this evolved once I started digging....