Jonathan Bate's fine book Soul of the Age: the life, mind and world of William Shakespeare, recently out in paperback, has an early section ('Give me the map there', pp 26-29, in the chapter 'The Discovery of England') which, although it doesn't mention King Lear, is interesting. He refers to the famous portrait of Elizabeth I by Marcus Gheeraerts the Younger (the 'Ditchley Portrait' - now in the National Portrait Gallery in London - details and copy here).
Bate discusses the importance of maps as 'instruments of power', and analyses the map on which Elizabeth is standing - Christopher Saxton's map of England from his famous atlas of 1579. See the image itself on the Glasgow University Library site here.
As Bate writes: It was the first ever accurate map of the whole country. It was one of the keys to the Elizabethans' discovery of their own land. To have in their hands a picture of every corner of England ... this was the dream of the men of power who set Saxton to work on his monumental surveying expedition ... Thanks to Saxton, the Elizabethans were the first England people to have a clear sense of the physical shape of their own nation. And that gave them a new sense of belonging.
All the more shocking then, for a monarch embodying the unity of the kingdom of Britain, to divide his kingdom, and start a process that results in that kingdom fragmenting into civil war, just as Lear's own heart breaks into 'a hundred thousand flaws' in his madness and grief.