Essexia Comitatus.

Double-page attractive map of the country of Essex. Showing London in the lower left corner, and other towns such as West Ham, East Ham, Waltham stow, South end on Sea, Harwich, Claxton, and the rivers Thames, Stour, Colne, Blackwater, Lea and Crouch. With kings' coats of arms and family coats of arms, last is empty along left border. On verso an illustration of prehistoric burying place.
French text on verso.
Taken from Joan Blaeu's French edition Le Theatre du Monde, ou Nouvelle Atlas, Mise en lumiere Par Guillaume et Jean Blaeu Quatriesme Partie. Amsterdami, Apud Iohannem Blaeu. MDCXLV. 1645. volume IV. The fourth volume of his atlas focused on England and Wales. Blaeu established his firm in 1599 as instrument and globe makers. He went on to produce some of the highest quality atlases ever published.
Willem Janszoon Blaeu (1571-1638) was the founder of the Blaeu publishing house. In 1634 he commenced publication of the "Theatrum Orbis Terrarum" or "Novus Atlas" and on his death he was succeeded by his son Johannes (1596-1673). Johannes continuously enlarged and updated the "Theatrum" up to 1658, including the addition of a separate volume devoted to England and Wales. Blaeu maps are renowned for the consummate care and attention apparent in every stage of production - using only the best paper with finely engraved plates and a high standard of printing. The county maps have decorative title cartouches and often depict the coats of arms of those families with important county links.

Reference: Koeman I, Bl 42 A (20)