Ships sailing parallel, representing Indonesia and Malaysia, amidst nautical charts.

Maritime Boundaries: How Indonesia and Malaysia Negotiated Their Seas

"Explore the untold stories of maritime boundary negotiations between Indonesia and Malaysia, shaping Southeast Asian geopolitics."


The seas between nations are not just bodies of water; they are zones of resources, strategy, and sovereignty. For Indonesia and Malaysia, two Southeast Asian giants, defining these maritime boundaries has been a decades-long endeavor filled with diplomatic maneuvering, technical challenges, and the ever-present specter of historical claims.

In 1969, as the world watched the space race and cultural revolutions, delegations from Indonesia and Malaysia gathered in Kuala Lumpur. Their mission: to negotiate the continental shelf boundary between them, an issue that touched upon the Straits of Malacca, the South China Sea, and the Sulawesi Sea. This was not merely about drawing lines on a map; it was about defining future access to resources and solidifying national identities.

This article navigates through the intricacies of these negotiations, drawing upon historical documents and expert insights to reveal the hidden layers of these critical discussions. Discover how individuals like Admiral Adi Sumardiman, armed with maps and legal acumen, played pivotal roles in shaping the maritime landscape we know today.

Charting the Course: The Initial Deliberations of 1969

Ships sailing parallel, representing Indonesia and Malaysia, amidst nautical charts.

In September 1969, representatives from Indonesia and Malaysia convened in Kuala Lumpur to address the complex issue of their shared continental shelf. The negotiations spanned four critical areas: the Straits of Malacca, the eastern and western sectors of the South China Sea, and the waters off East Kalimantan and Sabah in the Sulawesi Sea. The Indonesian delegation included legal and technical experts, with Admiral Adi Sumardiman, a Geodetic Engineer, leading the technical team.

Admiral Sumardiman’s role was critical. Tasked with discussing the precise course of delimitation lines, he had to reconcile geographical data, hydrographical surveys, and historical maps. One of the initial challenges was the differing datums used in Malaysian maps (based on British surveys) and Indonesian maps (based on former Netherlands East Indies surveys). This discrepancy required careful examination to ensure fair and accurate delimitation.
  • Initial Agreement: Both sides agreed to a median line approach for delimitation purposes.
  • Technical Teams: The Indonesian Naval Hydrographic Office and the Malaysian National Mapping Department formed teams to designate line coordinates.
  • Key Participants: Major Oemarijoto and Mr. Soembarjono from Indonesia worked alongside Mr. Hadji Yatim and Kok Swee Tuck from Malaysia.
Two significant problems emerged during the construction of these lines. First, Malaysia questioned Indonesia's use of three outermost islands—Batu Mandi, Tokong Pyramid, and Tokong Burung—as base points, arguing they were not included in Indonesia's Act No. 4 of 1960. After considerable discussion, the Malaysian side conceded. The second issue involved the dividing line in the northern part of Tanjung Datuk, where Malaysia had already entered into a concession agreement with Shell Oil Company, complicating adherence to a median line.

From Disagreement to Delimitation: The Long Road to Maritime Accord

The maritime boundary negotiations between Indonesia and Malaysia were a complex interplay of historical claims, technical data, and geopolitical considerations. Individuals like Admiral Adi Sumardiman played pivotal roles, navigating through cartographic discrepancies and sovereignty disputes. While challenges remain, the collaborative efforts underscore the importance of dialogue and diplomacy in resolving maritime issues, setting a precedent for future negotiations in the region and beyond.

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