The Atlas was first published in 1837 (Essex is dated 1835), and then several times to 1870 (or later), as Hobson's Fox Hunting Atlas (1850 to 1880), as Walker's fox hunting atlas and as Lett's Popular Atlas (1884 & 87). The maps were also published separately, dissected on cloth and folded up between boards, as in this case.
The Hundreds are still listed, with their numbers printed on the map, but the areas shown edge-coloured are the Parliamentary Divisions that were introduced in 1885. There is a paper slip pasted over the old list of election places to number the 8 Divisions across the county, plus the two "Borough" Divisions, Harwich and "Westham" - which is listed as having 2 MPs. In fact there were two Divisions - North West Ham and South West Ham - of one MP each.
Published by Longman & Co Paternoster Row, and [by J&C Walker ?] 37 Castle Street Holburn - on sheet within front cover. Also stuck on label of Edward Stanford, 26 & 27 Cockspur Street, Charing Cross, SW.
Scale correct at 1+12 miles = 82.5mm, or 4.0 miles/inch, ie 1:255,000.
The red line from Wendons Ambo to Bartlow (authorised 1863; opened 1867) now has an underlying (thick?) black line. There is a red line (no underlaying black) from Thorpe-le-Soken to Clacton (1877; 1882), plus from Southend to Shoeburyness (1882; 1884), from Brentford to Wickford (1883; 1888), and to Southend, Maldon and Tillingham (should have been to Southminster - all 3 authorised 1883, opened 1889).
There is a red line over the old black quad line from Grosvenor House to Walthamstow (1864; 1870), and then solely as a red line from Walthamstow to Chingford (1864; 1873); the Walthamstow line also heads SW then S to Bethnel Green (not named - 1864; 1872). The red line from Marks Tey to Sudbury (1846; 1849) now goes into and out of Sudbury correctly, whilst the old black quad line (incorrect) is still present.
There is also a red line for the never-built Burnham to Tillingham; the Grays-Thurrock to Upminster (1883; 1892) and Upminster to Romford (1883; 1893) are not shown. The old incorrectly shown lines are still present on the plate - in increasingly faint black.
This is thus a folded map that has 1861 population printed on, but a stuck-on label listing the 1885 Divisions and quoting 1881 population. It has many railway lines in just red, so estimate underlying map as 1871, updated to 1889 for newly opened lines. The origination date of the underlying map is c.1873 plus c1885+ for the litho transfer including the new Parliamentary Divisions, and a sale date of c.1889.
Many J&C Walker maps are shown on the Walker's Map Publisher page.