How did OSM draw the border line between Cambodia and Thailand?

General talk
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1

Hello everyone,

Cambodia and Thailand fought two deadly wars in 2025 because of the conflicting border demarcation that wasn’t accepted by either country. This comes, on one hand, from the French-Siamese maps at a 1:200,000 scale from the 1907 treaty, and on the other hand, from recent Thai maps at a 1:50,000 scale from the L7017/L7018 Series.

The border line drawn by OSM is noticeably different compared to the French-Siamese and Thai maps.

I’d like to know how OSM drew the border line between these two countries?

2

all the initial boundaries came from imports of data sources available at that time. Maybe VMap0. In the forum I did not find discussions on the country boundaries. I think this was pre-2010. Likely, this pre-dates the Thailand forum and mailing list existence. You could try your luck in searching the mailing list archives. talk is a good candidate.

I recall, that we later added better province-level boundaries and manually fixed the boundaries where it followed landmarks like rivers visible on Landsat imagery.

3

Hi @sunsoriya and welcome here,

please have a look at Disputed territories - OpenStreetMap Wiki too.
There is this border mentioned .

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4

Hi All,

Thanks for you reply.

OpenStreetMap, in this case of Border conflict that lies on a more than a century uncertainty of Border demarcation, must stay neutral and be cautious on drawing the border line as it has been currently published on OSM basemap. At least a cautionary mention should be added somewhere to indicate to the users that the current border line is under “Disputed Boundaries”.

Under the acutal fragile Ceasefire between these two countries, two things could be considered from OSM stand point :slight_smile:

  • OSM should be as impartial and credible
  • OSM should not fuel the war that might break out again because of the confusion created by OSM.

Could someone tell me what is the OSM Instance that could take the decision on this case of border dispute ?

Thanks you all

Soriya

5

Only a few OSM renderers support special rendering for disputed boundaries. This does require special tagging on these boundaries about who claim it and who dispute it. Such data does not yet seem available in the OSM database for this border conflict. You can find more information at the top of the aforementioned wiki page.

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Hi,

Thanks a lot for pointing me to OSM WIKI Page. The indicated link to border dispute between Thailand and Cambidia is not accurate. relation 19416764. It shows something to somewhere else.

To my knowledge the whole border line around (900Km) can be tagged as border dispute.

7

Another question to the OSM Community :slight_smile:

Are there groups of OSM experts which have the mandate to draw/redraw(update) border line for OSM ? If Yes, how can I follow the discussion/work of the group working on Thailand, Laos, Vietnam, and Cambodia ?

Thanks you all for taking time to answer this question.

Soriya

8

this is because the linked object does not exist anymore, it was deleted by the DWG.

9

Not really. Though before making edits, especially in case of known disputes, extra care needs to be taken.

And usually other edits will be more productive.

10

It looks like one year ago, user @Kri_ttt attempted to enter two specific disputed areas in the OSM database (rather than treating the entire 900 km border as disputed): Prasat Ta Muen Thom Disputed Area and Prasat Ta Krabey Disputed Area.

Subsequently, somebody sent a complaint to the Data Working Group (DWG) claiming the ‘edit was wrong’. The DWG then asked the original user whether their edit was correct or whether it should be reverted. The original user then opted for reversion because of the sensitivity of the issue, and hence the DWG performed the reversion.

It remains unclear whether that now reverted edit was actually correct or wrong, and why. Maybe further discussion in this topic can shed more light on the extent of the dispute so that this information can be properly entered in the OSM database.

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11

thank you for the summary.

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Hi,
You have pinpointed exactly the right hot disputed areas: Prasat Ta Meun Thom and Prasat Ta Krabey. Weird and tricky situation : someone has tried to modify the OSM database.

Could someone on DWG confirm whether the OSM database rollback had been made correctly?

I concur with you that we need to trigger the discussion on the border disputed between these two countries and to see how we can update the OSM database correctly later. Please tell us how we can do so. I will contribute to this task.

The most conflictual area is on the Dangrek Range : Mountainous area north of Cambodia about 400 km long. The most promising tools that can help us is to use SRTM/DEM to redraw this border line.

13

The DWG ticket was “Ticket#2025080110000374”. If you’d like to send a message to the DWG about this ticket, email data@openstreetmap.org with a subject line of “[Ticket#2025080110000374] forum” and it’ll ping the person from the DWG who dealt with the original ticket.

I’d suggest that you try and explain (perhaps by linking to historical OSM data) what the OSM data was like before, what it was like afterwards and why one of them was wrong and why. See here for some Overpass information that might help.

14

If you look at the actual changeset, only a couple of minor sections of the border change were reverted. See OSMCha for a view of what was changed.