GIS Files 2: Geographical data

2.2: Surveying and remote sensing (1)

Surveying techniques have undergone a remarkable process of evolution. Modern survey technology is extremely complex. Here we illustrate the most significant advances.

Early surveying techniques

In simple terms, the job of the surveyor is to measure the size, shape and relative location of physical objects in the outside world. Size and distance are fairly easy – you can use physical measuring tools of stable and constant length to record these dimensions. Some of the earliest long measurements were made using glass rods end to end, to fix a distance between two points on the ground. Such rudimentary methods are still in use today.

From the earliest days of surveying, surveyors have exploited the rules of trigonometry to deduce distances between points on the ground without actually having to measure them directly. Once you have accurately recorded the distance between two points, you can then identify the distance to any third point by simply measuring the angles between all three. This process is called triangulation and was the basis for Ordnance Survey's original creation of detailed mapping for the whole of Britain. The theodolite was the traditional optical tool used to survey in this way, and more recently electrical devices were developed to conduct this kind of ground measurement.

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