Meet the family visiting 90 triangulation pillars in a year

Have you ever wondered what the concrete structures at the top of mountains and hills are?

That's a question Press Packers Abigail and Joseph also wanted the answer to.

They did some research and found out that they are called triangulation pillars or trig pillars.

A triangulation pillar marks the highest part of the land, and were vital in map making when they were installed back in 1936.

As the first trig pillar was used on 18 April 1936, the brother and sister set themselves a challenge to visit 90 trig pillars before the pillars' 90th anniversary.

Abigail and Joseph began their challenge on 18 April 2025, so they had exactly a year to tick 90 off their list.

They have been using their weekends and school holidays to travel to new places and visit more trig pillars at the same time - even spending Christmas Day, and part of Abigail's birthday, doing the challenge.

They told Newsround that their favourite moment was when they climbed Yr Wyddfa - the Welsh name for Snowdon - before sunrise.

Sometimes the trig pillars were well hidden by bushes making them hard to find, but on a trip to the Peak District they managed to visit six trig pillars in one day.

They have now visited 89 and are aiming to reach their 90th trig pillar on 18 April - the anniversary itself.

Each pillar is generally around 1.2m tall, with a large part of the pillar buried below the ground.

The pillars were installed by the Ordnance Survey (OS), an agency responsible for creating and making sure that maps of Great Britain are as accurate as possible.

They are shown on a map as a small blue triangle symbol.

The pillars were designed by the OS to help separate the country into a network of triangles.

From each trig pillar you should be able to see two others, creating the triganular shape.

On the top of a trig pillar is something called a spider, where old surveying instruments would be placed.

Using this equipment the surveyor could take measurements and angles of the other trig pillars, to accurately map the land.

Trig pillars are not used today, as the OS has been able to make use of technology to find more modern ways of mapping the land.

OS Field Surveyor Alfie Turner explained to Joseph and Abigail that he uses a GNSS (Global Navigation Satellite Systems) receiver to pick up signals.

This technology is able to take very precise measurements and allow for 3D positioning for boundaries and terrain mapping, with more than 30,000 features being updated each day.

Alfie added: "We also have a drone team which are able to capture imagery, and a plane which flies over Great Britain, and we use that to update the map".