# How to find the coordinate system used?

I have a list of coördinates that are in X/Y form, and I need them in lat/lon. I tried googling around a bit, and found this method: Converting projected coordinates to lat/lon using Python?

This does seem to work, but I found out a few minutes ago that there are numerous coordinate reference systems, and I have no clue which one my data is in.

I tried a few of these: https://epsg.io/?q=Belgium (because the file I got is from a Belgian company), but the results I got didn't seem right.

Is there any way to figure out what coordinate system was used (except for trying out all 10000 possibilities), with a known combination?

For example, I know X="0511245565" Y="0042422978" should approximately equal to 51.206728, 3.253426 in wsg84.

My appologies if this has been asked before, or if this is a dumb question. I have no background in GIS, or anything related.

• Do you know the bounding box of the data, and the approximate lat-long bounding box you expect it to be? And what's the range of the data numbers - is it likely to be metres or km or furlongs? Try common ones first - EPSG:3857 (Google's Web Mercator) and the UTM zone for your area. – Spacedman Jul 19 '18 at 13:43
• But the real solution is to ask the people you got the data from - especially if they want you to do something with the data for them! – Spacedman Jul 19 '18 at 13:44
• @Spacedman: These seem to be somewhat the extreme values: X="0505440460" Y="0044309962" and X="0511002690" Y="0030139468" I think it's likely metres, but I'm not really sure how I can tell. EPSG:3857, isn't that the same as Google's wsg84? Isn't this the one I want as my target coordsystem? I tried a few of the Lambert ones (common in my area), but will try a few more. Yes, the easiest way would be to ask the person I got the data from (which is what I'm doing now, by mail), but I'm pretty sure that his answer will be "I don't know what you're talking about. I just use the data." – Opifex Jul 19 '18 at 13:50