Surveying

History of Maps and Cartography

Course 1 · Chapter 6 · Surveying the Nation

Until the eighteenth century most maps of a country were built from older maps, local knowledge and reports. Then states began to pay for measured surveys of their whole territory, using triangulation, a chain of precisely measured triangles, to make a framework on which detail could be hung. The map became an instrument of government, defence and taxation. This chapter looks at France, Scotland, the Ordnance Survey and India. Names and dates are from general knowledge and flagged "check".

How Triangulation Works

A baseline

Surveyors measure one length very carefully on level ground, often with chains or rods (check the methods used in each survey).

Angles

From each end of the baseline they measure the angles to a distant point, which fixes the triangle. The new side becomes the base of the next triangle, and so on across the land.

Detail

Once the framework is fixed, surveyors fill in roads, rivers, buildings and relief within it, working with smaller measurements. Errors are checked by closing the network.

Four Surveys

Survey (check each)Detail
The Cassini family map of France, 18th centuryA multi-generation project, begun under Louis XV, that produced the first map of a whole large country based on triangulation. The work showed that the Earth is slightly flattened at the poles, which was a scientific argument at the time (check).
The Military Survey of Scotland, 1747–1755Directed by William Roy after the Jacobite rising of 1745, it mapped the Highlands and much of the Lowlands for the army. The "Roy map" was not published in his time, and is a manuscript now held by the British Library, with a digital version online (check).
The Ordnance Survey, from 1791Founded as a military body, in the Board of Ordnance, and began with a baseline on Hounslow Heath, measured under Roy's plans. Its first map was of Kent, published in 1801 (check).
The Great Trigonometrical Survey of India, from 1802Began under William Lambton and continued under George Everest, a vast chain of triangles across the subcontinent, used for administration and as a basis for measuring the height of the Himalaya (check).
Maps and power These surveys were paid for by states for reasons of defence, tax, land ownership and control. Roy's survey followed a rebellion, and the Great Trigonometrical Survey served a colonial government. The maps were also scientific achievements. Both statements are true and a good history keeps them together.

The Ordnance Survey

  • Scales. It mapped Britain at a series of scales, and the "one-inch" maps became the best-known (check the history of scales and the later switch to metric).
  • The "Battle of the Scales." In the 1820s and after, there was a dispute over which scales to use in Ireland and Scotland, in which cost, accuracy and uses of land records were weighed against each other (check).
  • The Ireland survey, from the 1820s, produced detailed six-inch maps and a record of place names (check).
  • Heights. Bench marks cut into stone record heights above a sea-level datum, and many can still be found on old buildings (check).
  • Today. The agency is now Ordnance Survey, a government-owned company, and supplies both paper and digital maps (check its current status).

Scotland, India and Everest

ItemNote (check each)
Roy's mapDrawn at a scale of about 1 inch to 1000 yards and coloured by hand, it shows farm buildings, fields, roads and hills in detail.
George EverestSurveyor General of India from 1830 to 1843. The mountain was named after him in 1865, although he is said to have objected to the idea (check the story).
Local surveyorsMuch fieldwork depended on Indian surveyors and assistants, some of whom trained for secret surveys across the border. Their contribution was long under-credited (check).
Place namesSurveyors recorded names from local informants, which sometimes created errors or standardised spellings.
A British comparison The National Library of Scotland's online maps let a reader compare Roy's survey with the Ordnance Survey and with a present-day map of the same ground, so that a place in the Highlands or the Pentlands can be traced across 270 years. Edinburgh readers can often see what has changed by comparing the same square on each (check what is on the site).
Check the details Check dates, scales and the order of events in each survey. The story that Everest disliked the naming and the details of his career should be checked with an authoritative source.

Exercises

Exercise 1

Explain triangulation as if to a friend who has never heard of it, with a diagram you can describe in words.

→ Solution
Exercise 2

Compare the purposes of Roy's survey and the Great Trigonometrical Survey. What did the maps' patrons want, and who gained?

→ Solution
Exercise 3

Using an online map library, compare one square kilometre of your area on an old Ordnance Survey sheet and on a modern map, and list five changes.

→ Solution

Quick Reference

  • Triangulation: baseline plus angles, then detail
  • France: Cassini map, first national triangulation (check)
  • Scotland: Roy's Military Survey, 1747–1755
  • Britain: Ordnance Survey from 1791
  • India: Great Trigonometrical Survey, Everest