When the likes of Admiral Zheng He (Cheng Ho) and Sir Stamford Raffles sailed the seas, they relied on maps drawn by experts who used the stars as reference points.
Today, hydrographers use lasers, drones and a whole horde of electronic devices to measure the nature of large bodies of water, including what lies beneath. These can include rivers and lakes, and the charts help ensure safe navigation.
Dr Parry Oei Soe Ling, 60, is the chief hydrographer of the Maritime and Port Authority (MPA) and has been in the post since 2004. Last year, he became the second Asian to be conferred the prestigious Alexander Dalrymple Award by the United Kingdom Hydrographic Office.
This was for his work in promoting and developing electronic navigational charts in Asia. But one of his most memorable moments was the role he played in the Pedra Branca dispute between Singapore and Malaysia in 2008.
Dr Oei said it involved a picture of the island the Malaysian legal team used as part of its sovereignty claim. "When the Malaysians showed pictures of the island, I remember everyone on the Singapore side looking to me for my opinion. The proportions of the lighthouse and the hills in the background looked wrong. I was sure of it; I've sailed past that lighthouse hundreds of times in my life," he said.
The International Court of Justice (ICJ) later awarded sovereignty of the island to Singapore.
This February, Malaysia filed documents with ICJ in a bid to overturn the judgment.
But Foreign Minister Vivian Balakrishnan said during the Budget debate last month that Singapore strongly believes the documents do not satisfy the criteria for a revision.
Dr Oei, who was awarded a Public Administration Medal in 2008, described himself as a scientist first. And, sure, he is proud of the role he played. On a wall in his office, Dr Oei, who is also the port services director, hangs three paintings of Horsburgh Lighthouse on Pedra Branca. One of them is a gift from former law minister S. Jayakumar, who was also deputy prime minister. Professor Jayakumar gave him the painting for his involvement in the Pedra Branca case.
But his job is to make sense of underwater dangers, leading a team of around 40 staff from his department at Tanjong Pagar Complex.
Half of them are hydrographers who head out to sea daily to perform surveys, and the rest are cartographers who convert the data into actual maps. Said Dr Oei: "Singapore's port is just a small jigsaw puzzle piece to the world. My job is to allow people to zoom into that jigsaw piece."
His interest in the sea stretches back five decades to his boyhood, when he would spend hours peering out at sea from his East Coast kampung. When he was 23, he signed on with the navy, serving as a navigational officer. Back then, he used Transit - the precursor of the ubiquitous global positioning system (GPS).
He joined the Port of Singapore Authority in 1982, as MPA was known then. "Unlike GPS, you had to wait three hours for a Transit satellite to pass overhead," he said, adding that the experience made him a firm believer of electronic navigation.
But championing electronic navigation is "an uphill task" as many seafarers still prefer paper charts or are reluctant to fork out for computer-based navigational systems, such as the Electronic Chart Display and Information System (ECDIS), said Dr Oei.
While many cars are now equipped with GPS devices, only half of all ships last year had the ECDIS - something that Dr Oei hopes will change.