Universal Magazine
The Universal Magazine was published monthly from 1747 until 1799, published by John Hinton until his death in 1781.
County maps were published from June 1747 until September 1766, and then a completely different set from 1791 to 1798.
Essex was published in January 1750, drawn by Thomas Kitchin (who was officially working for the London Magazine by then).
Scale correct at 10mls = 30.5mm, or 8.2 miles/inch, ie 1:515,000.