The New Large Scale Atlas of the British Isles
The most prominent feature are the bright colours for the Parliamentary Divisions, as used from 1885, which retained Colchester as a separate Division. There is "Essex 16" in the top right corner, its sheet number in the atlas.
More details on Bacon's maps are on the Publisher's page.
Scale correct at 10 miles = 63mm, or 4.0 miles/inch, ie 1:255,000.
The railway line from Upminster through Laindon to Pitsea is shown (authorised 1882, opened 1885/1888); there are also dashed lines from Romford to Upminster to Grays Thurrock (both authorised 1883, and opened 1893/92). There is no explanation of the dashed railway line in the key - in later maps there is explaining these as "in progress". There is an explanation given regarding the meaning for different fonts used for station names.