Gambia Highpoint

Sare Firasu Hill (50.905m +/- 0.067m), Gambia Highpoint
Location: 13.221566, -14.159756

Dec 18, 2021

Eric, Serge, Kahler

Background

Gambia is one of the few remaining countries in the world for which the location of the highest point was not known (before this trip). Gambia is a very flat, low-elevation country and has not previously been surveyed carefully enough to definitively determine the highest point. 

The country is a small sliver of land on the edge of the Gambia river, and is completely surrounded by Senegal except for a small border with the Atlantic Ocean. Legend has it the country border was established by cannonballs being shot from a ship as it sailed on the Gambia River, and wherever they landed was the border. This is most likely an exaggeration, but much of the border is actually defined as 10km north and south of the Gambia River. 

Knowing the exact border location is critical to determining the highpoint of the country.

I’ve been planning to do a careful ground survey in Gambia for a few years, with the goal of determining the location of the highest point. In March of 2020 I had purchased plane tickets, rented a survey-grade Trimble Geo7x surveying unit, and packed for the trip. But then the covid pandemic hit and I canceled the day before the trip was supposed to start. My tickets were still valid until the end of 2021, so I decided to try again in December 2021 with Serge and Kahler.

I first needed to research what elevation surveys had been conducted in Gambia to see what information I had to work with. Most online sources cite a location called Red Rocks as the highpoint, with an elevation of 53m.

However, Google Earth SRTM satellite surveys [5] show four locations with elevations greater than 60m, and one with elevation 59m. These are all officially unnamed, but I will refer to them based on the districts they are located in. They are Sare Bala Hill, Sare Doulde Hill, Sare Bissou Hill, Sare Firasu Hill, and Sare Sorry Hill. I found a digital elevation model (DEM) on topographic-maps.com [6] that agrees with the google earth data. I also purchased access to another DEM from floodmap.net [7] that agreed with the SRTM data. SRTM data can have errors up to 16m [1], so SRTM is not sufficient to tell which of the four candidates are highest. 

These are the only DEMs I was able to find. In general, ground surveys are often much more accurate than SRTM. I purchased access to the only three ground surveys I could find, a 1981 soviet survey and two US military surveys [2],[3],[4]. Unfortunately they only provided 10m topographic lines, so were also not accurate enough to distinguish between the top five candidates. 

Greg Slayden has done research into the Gambia highpoint and listed three of the top candidates on peakbagger.com [9]. His candidates matched the ones I had found with the exception of Sare Firasu Hill and Sare Sorry Hill.

The Sare Firasu Hill is near the village of Fass Bojang. Interestingly, the border in this region is shown differently according to different sources. Google maps, Bing maps, and the 1981 soviet survey show Fass Bojang is within Gambia, while Gaia, open street maps, caltopo, and a 1975 British map [11] show Fass Bojang is in Senegal. 

If the google maps/1981 Soviet survey border is correct, Sare Firasu Hill is on the Gambia-Senegal border and SRTM measures it as 65m. This is the highest candidate based on SRTM. But if the open street maps/1975 British survey border is correct, the Sare Firasu Hill is not in Gambia and not actually a highpoint candidate.

To resolve this I needed to determine the exact border location. Katie checked out the book “African Boundaries – A Legal and Diplomatic Encyclopaedia” [12] for me from the University of Washington library. This was written in 1979 and said for that area of eastern Gambia the border is defined as 10km from the south bank of the Gambia river, subject to adjustments. Sare Firasu Hill is 11km from the south edge of the Gambia River, so as long as there were no adjustments after 1979 then it would be completely in Senegal.

Greg pointed me to a 1975 British 1:50,000 map set [11], which is perhaps the most accurate made for Gambia. I purchased the relevant maps and had them overnighted to me since I was flying out soon. They showed the border 10km from the river, with Sare Firasu Hill squarely in Senegal. 

But could google maps and the 1981 Soviet survey really be wrong? I tried contacting google maps to ask about their sources, but they just told me to submit a request for correction, which I did but never heard back from. The Soviet survey was conducted two years after the Encyclopaedia border definition and six years after the British survey, so it was possible there was a border adjustment in that time.  

It appeared the only way to know for sure would be to go to the Sare Firasu and ask local farmers if their land was in Gambia or Senegal. I had read there was no fence on the border and only sparse border pillars, so it would likely be unclear exactly where the border was. But if I could visit those five candidates I would be sure to have visited the highpoint.

I really wanted to determine exactly which point of the five was the highest so the country highpoint location could finally be known. Of the five candidates, three were each 61m, one 65m and one 59m based on SRTM. Thus a ground measurement would likely need submeter vertical accuracy to definitively determine the highest point. 

I have a handheld Garmin 62S GPS which can get about 20m vertical accuracy, but that wouldn’t be sufficient. Phone GPS measurements are based on barometric pressure and are even less accurate. In 2018 Matthew and I had rented a Trimble Geo7x unit from Waypoint technology to determine the true highpoint of Saudi Arabia, and that unit was capable of sub meter vertical accuracy. It required a base station nearby, though, which might not be possible in West Africa.

I contacted another company which could rent me a Geo7x, but it would be expensive and they wouldn’t be able to help with post processing the data. Then I heard back from Compass Data. In 2015 they measured the height of Denali to get the most accurate height to date. They very generously offered to lend me a Trimble GeoXR with Zephyr 2 antenna capable of 3cm vertical accuracy with no need for a base station nearby. I would just have to take measurements for an hour to get that accuracy. That sounded perfect! 

The day before my flight the equipment arrived and I was able to take a practice measurement to verify I was using the equipment correctly. Everything was in place for the trip to go forward. This would be part of a larger trip to climb and measure the highpoints of eight West African countries (Togo, Ghana, Benin, Gambia, Guinea, Cote D’Ivoir, Senegal, and Guinea Bissau). 

In the few days before the trip it appeared new covid restrictions might thwart our plans yet again. The US changed its entry policy to require a negative covid test one day before flight departure instead of three days. This was problematic since our planned PCR test in africa to come back to the states could only guarantee a two-day turnaround time.

Fortunately, I discovered there exist self administered antigen tests from emed.com that only take 15 minutes and, if done in the presence of a telemed doctor, can be used for entry into the US. I bought a pack of six tests for $150 and we were all set for the trip.

Dec 16

After climbing the highpoints of Togo, Ghana, and Benin we landed in Dakar, Senegal in the evening of December 16. I had carefully planned the West Africa itinerary to start with Togo, then Senegal, then Guinea. This allowed the mandatory PCR test on arrival in Togo to count for the PCR test required to enter Senegal. (Senegal required a PCR test five days before arrival and we would only be in Togo four days.) Guinea required a PCR test within 72 hours of arrival and we would get this in Senegal. The only place in Senegal giving PCR tests for travel was the Pasteur Institute in Dakar. They guaranteed results within 48 hours.

Our plan was to get a test as soon as possible after we landed, then while waiting for results we would get all the Gambia highpoint candidates. Then we would return to Dakar and fly to Guinea for the next leg of the trip.

I usually like renting a car and driving on my own for trips like this, but I’ve discovered it often makes more sense in rural african countries to hire a driver. The reasons are price and safety. Rental agencies often charge a per kilometer fee in Africa and that can add up very quickly. If this is the case, hiring a driver is generally actually cheaper, surprisingly.

There are often police checkpoints in these kinds of countries, and they will ask for big bribes if the car is full of white people. I call these gringo fees. But with a local driver the police often won’t ask for bribes, or if they do the bribes will be much smaller.

Finally, a local driver will know which areas are safe and which are dangerous. They will also know if it is safe to drive at night, which roads will be passable, and what the expected driving times will be based on road conditions. (Google maps times are not reliable when roads are rough.)

Serge had already found a contact, Cellou, in Guinea, and Cellou connected us with Pepe in Senegal. Pepe had a 4wd SUV capable of handling rough roads and taking us and our luggage. He would drive and we would pay 70 USD per day plus gas.

We landed in Senegal at 430pm on Dec 16 and eventually made it through the customs and covid test checkpoint. Interestingly, shortly before our trip Senegal had relaxed its covid policy to allow fully vaccinated travelers to enter without a PCR test. So we were doubly covered with our vaccination cards and PCR test from Togo.

We met Pepe and then drove into Dakar. The roads were in excellent shape in Senegal, better than many US roads. There was a lot of traffic, though. Dakar is on a peninsula so all traffic gets bottlenecked through a small corridor and Pepe said it is usually bad.

We eventually made it to the Archotel, which I had chosen since it was close to the Pasteur Institute for our test the next morning. The testing center opened at 730, and didn’t take reservations. It was just first come first serve. Pepe said he had seen hundreds of people in line there before and advised we get there very early to not lose time. 

We ate a spaghetti bolognese dinner at the hotel then went to bed. 

Dec 17

The next morning Pepe met us at 530am and we soon got in line at the Pasteur Institute. There were already eight people ahead of us! Luckily they gave us each a piece of paper with a number on it so we wouldn’t worry about people cutting in front of us.

I dozed off in some chairs under a tent outside. Finally at 730am two doctors came and started calling numbers. By then at least 100 people were waiting around. The people with numbers one through five weren’t there and I imagine they had gone back to sleep and not woken back up in time. 

Eventually we got our tests taken, paid about 40USD each, got a website and code to enter to find results, and proceeded on our way by 8am.

We fought rush hour Dakar traffic for an hour but eventually made it out of town and were cruising on open road. It was great to have Pepe driving to navigate passing all the slow moving trucks while avoiding oncoming motorcycles.

We stopped in Koungeheul for a shawarma food break, and started strategizing about how to reach the five candidate highpoints. Four of them were each a few hundred meters inside Gambia and the fifth and likely lowest candidate was 2.5km inside Gambia. We weren’t sure if there was a border fence or border patrol in those areas. Pepe said he had all the paperwork to drive into Gambia, and the only covid restriction was a vaccination card was required (though not for locals). 

Pepe said he had driven into Gambia recently and there were lots of checkpoints where police expected significant bribes. That was when he was alone. With three white guys in the car the bribes would only go up.

We decided to try to access the locations from the Senegal side first, and if we encountered problems then our plan B would be access them from the Gambia side. 

The first candidate was the northeastern most hill near Sare Bala, Sare Bala Hill, a few hundred meters from route N6. We figured it might look suspicious to have the car parked on that major road while we took measurements for an hour, but luckily based on satellite images we knew there was a small dirt road paralleling the main road. 

Based on those images we directed Pepe to turn off before the point, then we drove on the dirt road to as close as possible to the candidate.

Pepe stayed with the truck while we quickly packed up gear and started hiking. We could actually follow a trail almost the whole way, with just a short bushwhack to the candidate. The border was completely unmarked- no fence or posts or anything. It appears locals just walk back and forth as if it were a state border in the US.

The ground was pretty much level all around with maybe 10cm variations so we went to the exact coordinates of the SRTM highpoint and set up the surveying equipment there. 

Two guys passed by on a motorcycle on the trail but we waved at them and they didn’t seem to care. After starting the measurement we wandered around a bit and found a few termite mounds up to 10ft tall. They are made of dirt and we scrambled up to tag the tops of them, but I wouldn’t consider them candidates for the country highpoint. While they are made of natural material and aren’t constructed by humans, they are not quite natural since they are made by insects. If they counted then the highpoint might change year to year as some get taller and some fall over. The only real way to have a single consistent highpoint is if the termite mounds don’t count. Interestingly, I believe Gambia is the only country where this is an issue.

After an hour of measurements we packed up the equipment and returned to the truck. Nobody had cared that we were parked there or that we ventured 100m into Gambia. This was a pleasant surprise and we planned to try the same method for the other candidates. 

We had a bit of daylight left so continued to the next candidate, Sare Doulde Hill. We drove through Manda to the Sare Doulde area, then turned off on the nearest dirt road. Pepe stayed with the truck again and we hiked out with the equipment.

As before, there was no indication of where the border was. We followed a trail to a farmers field where the highpoint coordinates were and set up the equipment there. The ground was basically flat with 10cm variations as before. 

We set up the equipment in some tall grass to not be too conspicuous, but it was hard to not be conspicuous being three white guys hanging around in a field in Gambia. The local farmers came over and started talking to us. They spoke English (Gambia is a former British colony while Senegal is a former French colony) and confirmed we were indeed in Gambia. They were cutting grass for hay and just heading home for the night. 

We took some pictures with their donkey and they all wanted pictures with us. Somehow they never asked about the weird survey equipment, perhaps because we tried hard to keep talking about other things. They invited us to join them the next morning in the field but unfortunately we said we were busy.

It soon got dark and they headed home in Gambia. The father managed to fit six people on his motorcycle (himself and five children)! That’s the record most I’ve ever seen. After an hour had elapsed we packed up the equipment and walked the short distance back in the dark. We drove an hour to Velingara, and found a good hotel for the night. 

Dec 18

The next morning we ate breakfast at 530am and tried to determine whether our next candidate, Sare Firasu Hill, was in fact in Gambia or in Senegal. Our maps had conflicting information, but the town we were in was very close to the hill, so we figured the hotel owner might know.

We found the owner and I tried to say the name Sare Firasu to ask. I think my accent was weird and he had trouble understanding. So we got out a piece of paper and I wrote SARE FIRASU in big letters. 

“Ahh, Sare firasu. Part in Gambia and part in Senegal,” he said.

That was not the answer I expected. But I figured Sare Firasu is likely the name of the district so it could encompass both countries. According to my maps the location of the village Fass Bojang would really determine the country the hill was in. If Fass Bojang is in Gambia then the Google maps border is correct, but if Fass Bojang is in Senegal then the 1975 British map and open street maps are correct. 

I wrote out FASS BOJANG in big letters and slid the paper over.

“Ahh, Fass Bojang. Gambia,” the hotel owner said. 

That settled it. The Google maps border is correct and Sare Firasu hill is on the Gambia-Senegal border. We would have to visit it after all. Apparently there must have been a border adjustment since 1979 that altered the border in that area. The 1981 Soviet survey and Google maps correctly account for that adjustment. 

With that information we set out from Velingara heading north toward Gambia. We pulled up satellite images on our phones and navigated on dirt roads just before the border checkpoint to as close as we could drive. Then Pepe stayed with the truck and we continued on foot as it slowly got light.

We passed through fields of cous cous, some grass, then finally dirt fields to the highpoint location. The ground looked flat in all directions so I set up the survey equipment on the SRTM location of the highpoint and started taking measurements. 

We didn’t see anyone the whole time, and after an hour of measurements we packed up and hiked back to the truck. There were two candidates left but one was 2.5km inside Gambia and the other just 200m inside. 

Given that the one deep inside Gambia, Sare Sorry Hill was the shortest based on SRTM (our most reliable source) and it would be risky to sneak that far across the border, and it was logistically difficult to come in from the Gambia side, we decided to just measure the last candidate, Sare Bissou Hill. I would still consider this a very rigorous survey since we were surveying the four highest candidates based on SRTM. The line has to be drawn somewhere on which candidates to do ground surveys for and we were surveying all points higher than 60m based on SRTM. 

We headed west on the roads closest to the border on the Senegal side. We passed a few small villages and then reached a military checkpoint. We told the military man we were tourists heading to Linguedie village then returning that afternoon. That was true, though we didn’t mention we’d also be venturing a little bit farther. 

He took our passports and inspected them for a while and then let us go. From there we continued past Linguedie and turned north on small roads we’d identified on satellite images. We made it to within a few hundred meters of the border before the paths disappeared. 

As before, Pepe stayed with the truck and we started hiking across the open fields. We crossed old cous cous fields and a group of farmers in the distance bit nobody seemed to care. The border was completely unmarked as before and we soon reached the location of the highpoint. 

Like the previous candidates, this one, Sare Bissou hill, was in a flat area with no obvious highpoint. So we went to the SRTM coordinates and set up the equipment. The sun was getting hot by then so we rested under a nearby tree.

After 30 minutes a guy on a motorcycle stopped and waved at us to come over. I was worried he would get mad at us but I knew it was important to act confident and not guilty. We walked over and greeted him and he spoke English. We told him we were tourists hiking to the highest land in Gambia. 

He was friendly and said he owned that field and his name was Asman. He said his brother lives in Canada and he was very happy to tell us about farming in Gambia. He just finished harvesting cous cous and now he has peanuts planted. Then after he harvests those he plants grass.

 I told him about my grandpa farming in Minnesota. The big difference is in Gambia Asman can farm year round but in Minnesota my grandpa could only farm part of the year. I tried to explain there was too much snow the rest of the year but I don’t think he understood what snow was.

I was hoping to keep talking long enough that the survey equipment could run for the full hour. This seemed to distract Asman and he never even mentioned the strange equipment. He offered we could come see his friends harvesting cous cous but we were nervous about meeting too many people in Gambia when we really hadn’t crossed officially. 

We politely said we had to be going (the hour had passed) and Asman said no problem and we were welcome to hang out on his land as long as we wanted. 

I dismantled the equipment and we hiked back to Senegal and met Pepe back in the truck by noon. We had finished all our planned measurements with no problems and no delays, which was kind of surprising. So we started heading back toward Dakar. 

It was very hot driving back, 107F,  and we made it to Kahone by evening. We found a hotel there and I took an hour elevation measurement outside for Compass Data before going to bed.

Dec 19

The next morning we slept in and drove to Saly Portudal for lunch on the beach, then caught our 630pm flight to our next destination, Guinea. 

The measurement results are summarized below. Sare Firasu Hill is officially the highpoint of Gambia. Note- these are given as PPP ellipsoidal height results with 95% confidence interval (RMSE), as processed by Compass Data engineers using Online Positioning User Service. The ellipsoidal height measurements were then converted to EGM2008 orthometric elevation.

Contact me if you are interested in more details of the post processing or would like to see the raw data.

References

1. SRTM Mission Statistics, Nasa Jet Propulsion Laboratory, [Online] Available at https://www2.jpl.nasa.gov/srtm/statistics.html [Accessed December 2021]
2. 1981 Soviet Military 1: 200 000 ground survey, [Online] Available at https://mapstor.com/map-sets/country-maps/western-africa.html#gs–200k–(1980-1983)–preview  [Accessed December 2021]
3. 1974 US Joint Operational 1: 250 000 ground survey, [Online] Available at https://mapstor.com/map-sets/country-maps/western-africa.html#gs–200k–(1980-1983)–preview  [Accessed December 2021]
4. 1994 US Military 1: 500 000 ground survey, [Online] Available at https://mapstor.com/map-sets/country-maps/western-africa.html#gs–200k–(1980-1983)–preview  [Accessed December 2021]
5. Google Earth 7.3.4 (2021). [Online] Available at http://www.google.com/earth/index.html [Accessed December 2021]
6. Yamazaki D., D. Ikeshima, R. Tawatari, T. Yamaguchi, F. O’Loughlin, J.C. Neal, C.C. Sampson, S. Kanae & P.D. Bates, A high accuracy map of global terrain elevations, Geophysical Research Letters, vol.44, pp.5844-5853, 2017 doi: 10.1002/2017GL072874 [Online] Available at https://en-us.topographic-map.com/[Accessed December 2021]
7. Floodmap Digital Elevation Model, [Online] Available at https://www.floodmap.net/, [Accessed December 2021]
8. ArcGIS World Topographic Map, [Online] Available at https://www.peakbagger.com/, [Accessed December 2021]
9. Peakbagger, [Online] Available at https://www.peakbagger.com/, [Accessed December 2021]
10. Gaia GPS, [Online] Available at https://www.gaiagps.com/, [Accessed December 2021]
11. Gambia. 1:50,000. British OS – Overseas Directorate. 1975. Available at https://www.chartsandmaps.com/index.php?main_page=index&cPath=3_31, [Accessed December 2021]
12. Brownlie, Ian (1979). African Boundaries: A Legal and Diplomatic Encyclopedia. Institute for International Affairs, Hurst and Co. pp. 213–29.

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