The Four Summits of Bukit Timah

Summary: The Bukit Timah ridge contains four peaks over 140 m. From maps dating back to 1846, the presence of three of these peaks were already known. The highest summit which is commonly known as "Bukit Timah Summit" is the east summit (Official height, 163.63 m). I have recently measured the height of the West Summit to be 162.8m, or roughly about 0.8 m shorter than the East Summit. I also measured the height of the North Summit as 142 m. 

Figure 1. Portion of the 1855 Hydrographic Chart by S. Congalton and J.T. Thomson. The 'Bukit Timah' feature is represented by three separate peaks on the map [1].

In the 1846 Hydrographic Chart by S. Congalton and J.T. Thomson [1], Bukit Timah is represented as a group of three peaks. (Shown in Figure 1 is the 1855 updated version of the 1846 edition, which I can't get a high enough resolution screen capture of). Initially, one may easily miss these details or simply attribute this to some form of fictional artwork. However, when I counter checked with more modern topographical maps, it confirms that these features on the 1846 maps are real and significant and the three peaks really do represent the real terrain of Bukit Timah.   

On the 2005 1:25000 topographical map (See Figure 2) [2], one can distinctly see four summits over 140 m, which I have marked out in blue on the map in Figure 2. The four summits are roughly arranged in a ‘chair’ shape, and I shall term them the north (N), west (W), east (E) and south (S) summits. If you compare the two maps, the three peaks on the 1846/55 map looks like they are representations of the East, West and South Summits. 

Figure 2. Portion of the 2005 Topographical Map Of Singapore [2]. This map shows that there are four summits over 140 m on the Bukit Timah Ridge, which I have marked out in blue. The darker blue (W)est, (E)ast and (S)outh summits seem to correspond to the three peaks featured in the 1846/55 map of Figure 1.

So where are these three (or four) summits of Bukit Timah?

East Summit: Most people will be familiar with this summit. It is the prominently marked 'Bukit Timah Summit', with a nice shelter and a large rock summit marker (Figure 3). The East summit is the highest geographical point in Singapore and has been measured to be 163.63 m high in a GPS survey [3]. This summit is denoted as the East Summit 'E' in the map of Figure 2.

Figure 3. The 'Bukit Timah Summit' that most people are familiar with, with an altitude of 163.63 m. The summit will be termed as the East Summit here. The summit marker on the right is a popular selfie/wefie landmark, marking the tallest geographical point on the island. (photo taken 17-12-2020)

South Summit: Besides the East Summit, the most prominent summit is probably the South Summit. It is the most exposed peak and easily visible from afar. On this summit is where the VHF radio station and towers are (See Figure 4), hence making it easily identifiable. The only published altitude of this summit that I can find is 146.6 m which appears on a 1970 1:10000 survey map (See Figure 5) [4]. 

Figure 4. View of the Bukit Timah South Summit, from Hinhede Quarry. The summit is capped with the VHF radio transmission station and towers (photo taken 17-12-2020).

North Summit: Possibly because it is shorter and deeper in the ridge, the North Summit did not feature in the 1846/1855 maps. There is no published height of this summit that I can find, but one can estimate its height from the available topographical maps (for example Fig. 2 and 5). The contour lines suggest that the summit height is at least 140 m. My recent determination of its height will be reported below.

Figure 5. Portion of the a 1970 Topographical Map [1:2500] of the Bukit Panjang - Bukit Timah Nature Reserve [4]. Marked on the map are the (N)orth, (W)est, (E)ast and (S)outh summits. 

West Summit: The West Summit is the most intriguing one. On the 2005 topographical map (Figure 2), the contour lines suggest that this summit, though not marked, is more than 160 m. A further search led me to the 1970 topographical map [4] (Figure 5). On it, the East Summit (a.k.a. the accepted highest point of Singapore, 'Bukit Timah Summit'. See above) is marked as 533 ft (162.5 m), while the West Summit, although with no altitude marked, has a contour line at 540 ft (164.6 m). This seems to suggest that the West Summit is actually higher than the East Summit! This got me slightly excited. Could it be that all along, we had been misled into thinking that the East Summit is the highest, and unbeknownst to most, the West Summit is in fact the highest geographical point in Singapore?! Furthermore, the 1970 map is not the only one which had the West Summit taller. A 1978 topographical map [5] (Figure 6) also has a 165 m contour line around the West Summit while the East Summit is marked as 163 m.

Figure 6. Portion of the a 1978 Topographical Map of the Bukit Timah Area [5]. Contour lines are shown at 5 meter intervals.

Not being able to find any records on whether there have been any altitude measurements done at the West Summit, I decided the easiest way to answer the question of whether the West Summit is indeed higher than the East Summit, is to measure the summit heights myself.

Since the height of the East Summit is known (at 163.63 m), what I really need to measure is the relative altitude between the West Summit and East Summit. Although the two Summits are separated by only slightly more than 200 m, there is thick vegetation between them. Thus relying on a line of sight determination of their relative height is quite impossible. The simplest solution I thought, was to use barometric measurements to find the relative pressure at the two summits. The higher summit should have a lower pressure. It is the same reason why the pressure on top of Mt Everest is only a third of that at sea level.  

Fortunately measuring pressure is easily doable and can be achieved with very decent precision. It turns out that some smartphones have barometric sensors and can measure pressure, i.e. I can use these kinds of smartphones as portable barometers. I therefore purchased a pair of Samsung Galaxy S4 smartphones from Lazada and used them to do my barometric measurements (Figure 7). The Samsung Galaxy S4 contains a BMP180 barometric pressure sensor chip with an equivalent altitude precision of about 0.17 m [6]. I will skip the details of the calibration and exact measurement procedure and only present the results below. Do contact me if you want more details on how the measurements and data analysis are done.

Figure 7. My pair of portable barometers (Samsung S4 smartphones) on the ground at the West Summit collecting data (photo taken 03-12-2020). 

With the help of my nephew, I measured the relative heights between the the West and East Summit on two dates, 30th Oct. 2020 and 3rd December 2020. In Figure 7, I show a picture of the smartphones at the West Summit collecting data. The data was then processed and analysed. 

Results: It was determined that the West Summit is indeed shorter than the East Summit by 0.8 m (with an uncertainty of about 0.3 m). Using the known altitude of the East Summit as a reference, this means that the West Summit has a height of 162.8 +/- 0.3 m. The saddle point between the two summits was measured to be 148.2 +/- 0.3 m. So, as it turns out, the 'Bukit Timah Summit' is correctly the tallest geographical spot of the land, although the West Summit came really really close! 

A similar measurement was performed for the North Summit, and its altitude was determined to be 141.9 +/- 0.5 m. The saddle point between the West and North summits was measured to be 127.0 +/- 0.7 m. 

The South Summit is within the telecommunication facilities compound and I can't do any measurements there, so we shall have to rely on the information on the 1970 map (Figure 5). From the same topographical map, the saddle point between the East and West Summits can be estimated to be approximately 135.5 m.  

To summarize, the heights of the four highest summits of the Bukit Timah Ridge is given below in round brackets. The square brackets give the prominence of the summits, which is its height minus the saddle point with its parent summit (in this case, the East Summit). 

1. East Summit (163.63 m)
2. West Summit (162.8 m) [14.6 m] 
3. South Summit (146.6 m) [11.1 m]
4. North Summit (141.9 m) [14.9 m] 

Given this, can we then say that the West, South and North Summits are the 2nd, 3rd and 4th highest point in Singapore, given that Bukit Gombak Hill is at 139 m? That is a tricky question, and I do not want to wade into this argument currently. Perhaps some other time. 

Appendix: Directions to the Summits.

Figure 8. Map with roads and paths of Bukit Timah Nature Reserve and where the four summits are located (Blue Flags).

East Summit: From the Visitor's center, take the Main Summit Road all the way till you see the shelter and the large rock summit marker (Figure 3). You can't miss it. 

West Summit: From the Main Summit Road, branch off to 'Jungle Falls Path'. After about a hundred meters, you should see a map board (See Figure 9). Behind the signboard is a slight rise in the terrain. The West Summit is right there. The Summit is in semi-thick vegetation and there is no markers to mark the summit. 

Figure 9. Off the 'Main Road' on 'Jungle Falls Path'. You will see this map board after about a hundred meters. Behind the map board is a slight rise in the terrain where the West Summit is. 

South Summit: Being within the Telecoms compound, the South summit is off-limit to the public. You can only get to the guarded gate of the compound. This gate can be reached by taking the road that branches off from the Main Summit Road at Simpang Hut.  

North Summit: Take the flight of steps about a hundred meters away on the East Summit. The steps lead down to Renges Path which then joins North View Path after a junction with Seraya Path. From the junction, North View path will gently rise to a crest after about 60 meters, before tapering down. That crest is the North Summit (See Figure 10). 

Figure 10. The crest on the North View Path is where the North Summit is. Or to be exact, somewhere about the grounds right beside the path you see in the picture, is the North Summit. On the right, you can see where I have placed my Samsung S4 smartphones for the barometric measurements (photo taken 03-12-2020).

References

[1] This Survey Of The Straits Of Singapore, Is Respectfully Inscribed To The Honourable Colonel Butterworth, C.B. Governor of Prince of Wales Island, Singapore & Malacca, by his most obedient servants, Samuel Congalton, Comm: H. C. Steamer, Diana, J. T. Thomson, Government Surveyor, 1846. (James M. Richardson, London, 1846). Retrievable from National Archives of Singapore. For Figure 1, I have used instead the updated 1855 edition, Retrievable from National Archives of Singapore.

[2] Singapore Series L802 Edition 10 SMU [1:25,000 Topographical Map] (Mapping Unit, Ministry of Defense, Singapore, 2005). Retrieved from https://libmaps.nus.edu.sg/  

[3] From conversations with Mok Ly Yng. The plaque on the summit rock records that the GPS measurement was carried out by GPS LANDS (Singapore) Pte. Ltd. founded in 2000. So the measurement of the summit height must have been performed post-2000. 

[4] Singapore Instrumental Plot - Bukit Panjang - Bukit Timah Nature Reserve [1:2,500 Topographical Map] (Produced by Fairey Surveys Ltd. for the Government of Singapore, Singapore, 1970). Retrieved from National Archives of Singapore. 

[5]  Singapore Series SMU 010 Sheet 15 Edition 1 SMU [1:10,000 Topographical Map] (Mapping Branch, Ministry of Defense, Singapore, 1978). Retrieved from National Archives of Singapore. 

[6] https://www.eenewseurope.com/news/pressure-sensor-enables-altitude-accuracy-within-8cm