1 : 31680 .A triangulation diagram appears on the reverse of this drawing. This enabled the draughtsman to plot features of the landscape with precision.,A trigonometrical point is marked at Air Lighthouse at the top of the plan. Pencil lines radiate from this point, indicating the angular measurements taken from here. Archaeological sites are,labelled,in gothic script. ,'Tumuli' (ceremonial burial mounds) are marked in this way in several places. Durrant, William R
1 : 31680 A note in the bottom left corner of this drawing records the date it was received at the Drawing Office in the Tower of London, where final reduced copies of the plans were made. It is one of the few drawings to make reference to the Tower. A triangulation drawing appears on the reverse, along with an area calculation, referred to in its formal title. Major communication routes are highlighted in yellow, following standard military cartographic convention. Hughes, Herbert J.