1 : 31680 This plan covers a section of the Cambrian Mountains from Denbigh in the Vale of Clwyd, at the top, to the valley of the River Dee, which forms a boundary at the bottom right of the map. The drawing is formally titled and the area of the land recorded as 181.1792 square miles. Archaeological sites are named in gothic script. Colour washes depicting relief are combined with numerical annotations of altitude ('spot heights') in black ink. A key to interpreting the mineral content of the landscape survives just below the area calculation table. Entitled 'Mineral Notives', it uses symbols to distinguish limestone, red sandstone, greywacke slate and alluvium. Declivity ('downward tilts') in the land are shown in red by an arrow and angular value. Dawson, Robert
1 : 31680 A triangulation diagram appears on the reverse of this drawing. This enabled draughtsmen to plot the exact location of topographical features. Mileage is indicated on major communication routes, accompanied by abbreviations of the town names from which distance has been measured. For example, the abbreviation 'MS L''2' indicates two miles from Llangollen. Archaeological sites are named in gothic script. A triangulation grid is faintly visible in the left hand portion of the drawing, and pencil lines radiate from trigonometrical stations, marked by dots within triangles. Durrant, William R
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 This,original protraction is formally titled. The traverse routes are noted with the relevant dates and Ordnance Survey field-book page numbers. The conventional sign of a dot within a triangle indicates a trigonometrical point. These appear around the edges of the drawing in red ink,,marking the points from which the surveyor took angular measurements to plot features of the landscape. , Collard, Thomas W.
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.