London Magazine, August 1748
The London Magazine was published monthly from 1732 to 1783, and contained county maps at random dates between 1747 and 1763.
Essex was published in the August 1748 issue.
The maps were later issued as separate sheets, at 3d each, but these seem to have not sold well, as none have been seen.
Essex is not included in the Dublin re-printings of the London Magazine. These maps were reused by Walpole in 1787.
Scale correct at 9 miles = 39mm, or 5.9 miles/inch, ie 1:375,000.