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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
Erddig Wood, near Wrexham (detail from OSD Map 316 [Chester], surveyed in 1819)
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Detail from OSD 316, showing Wrexham and Erddig ('Erthig'),Wood to the south. The area to the west of Wrexham is not shown on this sheet. The whole,plan follows the meandering River Dee from Chester, at the top of the map, to Overton and Ruabon, at the bottom left. A section of the Shropshire Union Canal, running from Chester to Waverton, is shown in blue. At the bottom left of the map, an area calculation table survives in black ink. The pencil gridlines running through Chester were most likely guides for making enlarged or reduced copies of the map.