Scale Rule and Area Measuring Grids
Images courtesy of Abbie Gordon, Banchory.
Several survey plotting and map area measuring tools. The scale rule (top) was a key tool for converting the length measurements on the ground into line lengths on a map. Scale rules came in many types of unit measurement (feet, yards, metres) and in a large range of scales of which the 1:10560 was the standard for the 6 inch to the mile maps. After the 1980s the 1:10000 metric scale standard maps was adopted when Ordnance Survey maps of that scale became generally available for all areas.
The two plastic area measuring grids shown at the bottom of the image were very often used by field foresters to measure areas on the standard forest maps. To measure a compartment (or a part of a compartment) the grid was placed on top of the area and all the complete rectangles within the boundaries were counted and then in those rectangles only partially within the boundaries the dots or mini squares still within the boundaries were counted and divided by 10 to give hectares. The two lots of figures added gave a fairly accurate area. The two colours emphasised which grid required to be used for the 1:10560 and 1:10000 standard maps at a time when both these scale maps were in general use.
The distance scale on the edge of the plastic grid was also heavily used by the field foresters and staff.
More accurate area measurement was carried out using a specialised measuring tool called a planimeter which required a steady hand and some skill to use proficiently. It also cost several hundred pounds – quite a sum to disperse out to forests! In the early days these machines were kept exclusively within Conservancy drawing offices.
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