The small pencil markings at the edges of this drawing were used as reference points by the draughtsman from which to plot the area accurately. The road to Earl Stoke is marked "TG", meaning toll gate. The precision with which the survey records the road network is testimony to the military imperative of the Survey and is a major advance on earlier county maps. Running diagonally across the drawing is the Roman road from Bath, indicated by grey lines. The Kennet and Avon Canal and the Wiltshire and Berkshire Canal are shown in aquamarine, with each lock recorded, most notably on the section leading into Devizes. The canals were opened in 1810 to better exploit the resources of the Somerset coalfield, and are therefore contemporary with the survey of this drawing. The paper is watermarked JAMES WHATMAN TURKEY MILL KENT 1807.
1 : 31680 Although this drawing was surveyed six years before the obligatory inclusion of archaeological sites on drawings, several are featured. The most famous of these is Stonehenge, to the right of the drawing. Ancient camps, earthworks, castles and grave mounds ('tumuli') pepper the area, indicated by concentric shapes and a title in neat script. Their inclusion reveals the meticulous nature of the survey. To the right of the drawing, opposite Wishford, a trigonometrical station is indicated by a dot within a circle (annotated 'Col. Mudge's station' - Major-General William Mudge was Superintendent of the Ordnance Survey). This station denotes a point from which angular measurements were taken. In the right hand margin of the drawing a point titled "End of Base" marks the end of the Salisbury Plain baseline: an important measurement allowing for the triangulation of the area. Crocker, Edmund