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Land Survey Services

Survey Control Network

SLA established the land survey control network as the infrastructure to support the surveying work conducted by all land surveyors. The control network allows all land lots in Singapore to be geographically linked to each other and to the whole of Singapore.

We maintain 2 types of survey control:

  • Horizontal Control Network (x- and y-coordinates)
  • Vertical Control Network (height).

Horizontal Control Network
There are two levels of horizontal control: Primary control and secondary control networks. SLA names this the Integrated Survey Network (ISN) which was set up using Global Positioning System (GPS) technology.

The primary control network is made up of about 70 primary markers that are strategically located in Singapore, most of which are on top of HDB flats, to cover the entire area of the island.

The secondary control network comprises of about 4,000 secondary control points. These secondary markers are planted on the ground along major roads for easy access.

Vertical Control Network
is mainly made up of Precise Levelling Benchmarks (PLBM) that formed the primary levelling network in Singapore. There are about 600 PLBMs located at 1 km intervals along major roads. Vertical Control information is used by surveyors to determine heights of certain locations in Singapore.

Control Point Sub-System (CPS)
is the database system that maintains the location information of both Horizontal Control and Vertical Control. You can gain access to ISN and PLBM information from the internet via the Integrated Land Information Service (INLIS).

Differential GPS Data
SLA maintains a network of 5 Global Positioning System (GPS) reference stations. Surveyors can also access GPS reference station data from SLA for the purpose of carrying out ISN survey work. Please contact SLA at 6323 9829 or email to for more information on accessing GPS data.

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