Looks like they already use OSM.

Here's the full Google Translate translation. Skip down to "How are the maps made?" for the OSM part.

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In regards to
Minecraft® à la carte is an online service offered by IGNfab, allowing you to generate Minecraft® maps (or other similar formats like Minetest) from geographic data, namely:

for France, the National Institute of Geographic and Forest Information (IGN) and elements of its data catalog, in particular: BD TOPO®, BD CARTO®, RGE ALTI® and BD ORTHO®. This service also uses the data available from the Graphic Plot Register (RPG)

for Wallonia, the Wallonia Public Service (SPW) and elements of its data catalog, in particular: Continuous Cartography Computer Project (PICC), Walloon Hydrographic Network, Bati 3D 2013-2014 Administrative limits (Apn_AdRe), Occupation map du sol (COSW), Relief MNT 2013-2014, Anonymous agricultural plot

for the whole world (France and Wallonia included if desired), from Bing (satellite imagery service), OpenStreetMap (OSM) and layers of its Planet OSM database listed in particular on https: //wiki.openstreetmap. org / wiki / FR: Standard_tile_layer

The service can also use the IGN Autocompletion (via REST), SPW Geolocation (via REST), and Bing Locations services for geocoding.

• How it works ?

To generate a map, all you have to do is enter:

An address located in France, Wallonia or around the world. Once the location has been selected, the area corresponding to the area of the future Minecraft® or Minetest map (with a default size of 2.5 km x 2.5 km) is displayed. It is also possible to simply position yourself with your mouse on the desired location (and in this case, the area will be calculated from the center of the map).

A valid email address, which will be used to send you a notification, once your map is ready to be downloaded. You will then be provided with a link to retrieve a file (in ZIP format) containing your card data.

A platform and a card format depending on the version of the software you are going to use to use the card that will be delivered to you.

Advanced options are available to configure your request in more detail: choice of data sources used, themes selected and geometric characteristics desired.

After accepting the T & Cs, you will be able to generate your card (provided that the number of remaining generations is not zero at the time you wish to initiate the request). After validation of GDPR compliance and control code, the card calculation starts and you will immediately receive a first order confirmation email (if the email address entered is correct).

• Installation

Your map is stored in the form of several binary files which constitute a backup of the game. To install it, unzip the archive that you have recovered, and copy its content in:

Your card can then be loaded from the in-game saves screen (in Solo mode).

• Rules

Only one generation per user and per day is possible.

The total number of generations is limited per day. The counter is reset at midnight (French time - UTC / GMT + 1).

There is a fixed number of card release periods per day. The time of the next release is indicated under the counter indicating the number of generations remaining over the period.
00h00: you have 100 cards available.
8:00 am: you have the rest of the previous period as well as 100 more cards available.
4:00 p.m .: you have the rest of the previous period as well as 100 more cards available.

Once your card is generated, it will remain available to you for 72 hours. After this period, it will be deleted.

• Terms of Service

• Overview

• How are the maps made?

We have developed our own map generation engine to create Minecraft maps in Java Edition and Bedrock Edition and Education Edition format, as well as maps in Minetest format. Using the service's default options, maps are generated as follows for each requested zone:

Loading of a terrain model from the RGE ALTI®.

Loading of data from the CARTO® database (land use).

Loading of data from the TOPO® database (buildings, roads, hydrography, cemeteries, vegetation).

Loading of data from the ORTHO® database (color of the ground, color of the roofs).

Loading of data from the 2017 Graphic Plot Register (RPG) (crops, vines and orchards).

Generate a 250 meter buffer around the map to transition to the classic Minecraft world.

Generation of several map objects instead of the "spawn" to be able to find your way around.

Using other options, maps are generated in a similar way with the corresponding data from the SPW or OSM and the SRTM3 (to replace the RGE ALTI® on the world). It should be noted that the 90 m pitch of the SRTM3 available on the world can introduce, for Minecraft® maps with 1 m cubes, a strong jump in the representation of the relief inherent in the resolution of this altitude information and affecting the rendering of the map obtained in the game.

Each block represents a ground area of 1 square meter (or less), and the planimetric scale is not distorted (1 meter on the ground in reality = 1 block on the ground or more in the map). The altimetric scale is on the other hand "overwritten" on maps in Minecraft format as soon as the relief of the area is too high (Alps, Pyrenees, Massif Central, etc.), to be able to represent the entire area between levels 40 and 210 a classic Minecraft map (limit of 256 levels in Minecraft; in the case of the Minetest format where this height limitation does not exist, the maps are kept with the same scale by default (a cube is equivalent to 1 m in height) , or even exaggerated in altitude to bring out the relief of particular High relief maps (Geographic tab of the Advanced options menu).

You can adjust the scale during your map generation request.

• FAQ

Q. I ordered my card, but I still haven't received anything. Is this normal?
A. If you entered the correct email address, you should receive a delivery email. Depending on demand and the size of the card, delivery time can vary from a few minutes to a few hours, or even over a day.

Q. There are 0 generations available at the time I visit the site, what can I do?
A. The time of the next calculable card release is indicated on the site. Wait until that hour.

Q. Are the generated maps compatible with Minecraft Pocket Edition?
A. Yes. Minecraft Pocket Edition as well as Windows 10 Edition are now supported. All you need to do is select the Minecraft Bedrock format when you request to generate a map.

Q. I want to play on console. Is it possible ?
A. It depends on the type of console. Currently, we only support Xbox One and Nintendo Switch. We are working on the integration of the format specific to the Playstation 4. The Playstation 3 and Xbox 360 will not be supported due to technical constraints (limited surface area on these consoles).

Q. What areas are currently supported?
A. The service covers mainland France, the following overseas territories: Martinique, Guadeloupe, Reunion Island, Mayotte, French Guyana as well as Saint-Pierre and Miquelon, Wallonia via the SPW, and the whole world via OpenStreetMap.

• Contact

For any information, please write to us at the following address: Contact us.

• Cookies and statistics

In order to adapt the Minecraft® site to the map to the demands of its visitors, the IGN measures the number of visits, the number of pages viewed as well as the activity of visitors to the site and their frequency of return. Piwik, the statistics tool used by IGN, generates a cookie with a unique identifier, the retention period of which is limited to 13 months. The tool used also collects your IP address, in order to determine the city from which you are connecting. This is immediately anonymized after use. The IGN can therefore under no circumstances trace this back to a natural person. The data collected is not transferred to third parties or used for other purposes.

Here you can choose NOT to allow tracking of your computer via a cookie assigning it a unique identification number. Our web analysis tool will not record your computer's activity.
To make this choice and install an opt-out cookie, please click below.

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Found a video of this Minetest thing they mention.

https://youtu.be/DXJBFHOXZGY

and these

https://wiki.minetest.net/Minetest/fr

https://www.minetest.net/