Trig Pillars, A Theodolite & Survey Tools: Mapping The World

It may be hard to remember the days before Global Positioning Systems, but this technology only has been available at large for about 20 years. Of course, we’ve been using maps for thousands of years, so tools such as trig pillars, theodolites, survey compasses and more were essential. Here’s a quick look at how we mapped the world prior to the invention of GPS.


Obviously, we still use theodolites for survey tasks today, and you see people on construction sites and roads every day using these devices. The theodolite has long been a handy device for measuring vertical and horizontal angles.

Theodolites are fairly large and heavy, so it might surprise you to learn that these actually were packed along with a variety of other surveying equipment for Lewis & Clark’s expedition through the Louisiana Territory. In fact, Thomas Jefferson lent the expedition one of his own theodolites, which was crafted by Jesse Ramsden.

Ramsden created the “Great Theodolite,” which was used to help create accurate maps of the United Kingdom by the Ordnance Survey of Great Britain. While it was quite large and 200 pounds in weight, it could provide sighting for up to 70 miles, which was quite impressive and, to put it into perspective, this is a distance greater than the English Channel Tunnel, which is 31 miles long.

Noticeably, the theodolite that Lewis & Clark used was far lighter than 200 pounds, but it was still a crucial piece of equipment. With the theodolite, survey tasks definitely are much easier to handle.

Surveyor’s Compasses

This device, sometimes called a circumferentor, was a very handy tool for early surveyors, and like the theodolite, survey tasks often still require the use of these compasses. These were invented in the 17th century and could be used to measure angles in the horizontal plane as well as determining the direction of a line in relation to the magnetic north pole.

Surveyor’s Chains

While tools such as the theodolite and survey compass could help one determine angles of slope and fairly accurate distance estimates, if you truly needed to know the exact distance between two points, one might employ the use of a surveyor’s chain.

There were several versions of surveyor’s chains used in the past. They most commonly used type was a Gunter’s chain, which included 100 links in the chain, and each link in this chain measures 7.92 inches long for a total length for 66 feet. 80 of these chains equal 5,280 feet, otherwise known as a statute mile.

Of course, hauling around 80 of these surveying chains wasn’t an option for many large-scale cartography projects. In fact, Lewis & Clark were said to have simply brought a two-pole chain, which is a surveyor’s chain that is just 33 feet in length. This could be used to help establish a baseline measurement for triangulation tasks, such as determining the width across a river.

Octants & Sextants

When you think about devices such as octants and sextants, sea voyages are more likely to spring to mind than land surveying. However, these can be useful when one needs to determining latitude. For instance, back to Lewis & Clark, Meriwether Lewis would use the octant to view the horizon in relation to the sun or another star. Obviously, when making a map, noting the degrees of latitude and longitude is an essential part of the process in order to ensure accuracy.

Spirit Levels

This is another fairly simple tool that was included in the many surveying instruments toted along by Lewis & Clark. We use spirit levels, sometimes known as bubble levels, all of the time for many household tasks, such as hanging pictures. For surveying, a spirit level could be used to ensure that a surveyor’s compass was level, or it could be used to create an artificial horizon.

Trig Pillars

These are fixed pillars that are used for triangulation tasks. Triangulation, as you probably know, is a process in trigonometry that can be used to measure the distance between two points. Trig pillars would help a person using a theodolite for survey and mapping tasks.

In Great Britain, for instance, thousands of trig pillars were placed at points all over the country to help with a huge mapping project undertaken by the Ordnance Survey in the 1930s. About 6,500 trip pillars were constructed and used and many still remain, although trig pillars are no longer needed for triangulation (thank you GPS).  As for Warren-Knight, we’ve been creating navigation and surveying instruments for more than 100 years, and we still produce quality theodolites, survey compasses and much more. Take a look at our selection, and if you don’t see precisely what you need, give us a call. We may be able to provide you with a custom solution.

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