# Figure out which coordinate system being used

I'm working in a project that have no documentation and I'm trying to figure out which coordinate system is being used in their API. What I know is that they have a coordinate like this:

```latitude: -12168371
longitude: -27370165
```

And this maps to somewhere near this coordinate in the EPSG:4326 system:

```latitude:-20.274378
longitude:-45.62233
```

Is there any service/clue/process that could help me find which coordinate system is being used?

• Do the points appear to be over the whole globe or are all the points in a small area of lat-long? What's the numeric range of the coordinates - could it be metres, centimetres, miles, feet? I couldn't get any joy out of projfinder either but sometimes scaling the units knowing its miles and proj uses km helps. More detective work needed! Jan 5, 2020 at 15:34
• Looks like the lat / lon were multiplied by 600,000. If I divide your numbers by 600,000, I arrive at -20.2806183, -45.6169416, near the point you mention in Calcario Cazanga mining site in Arcos, Brazil. If you apply this logic to all your coordinates (divide them by 600,000), and then assign epsg 4326, does it work? Jan 5, 2020 at 22:20
• @FSimardGIS How did you get to this idea of dividing by 600,000? Jan 6, 2020 at 18:05
• @TomazicM I've seen cases where latitudes and longitudes were expressed in milliarcseconds, arcminutes, etc, so I figured I could check this out by dividing both coordinate pairs and see if the result matched a nice round number beginning in 60 or 3600. In this case, it looks like the units might be derived from arcminutes, something like this: Latitude = -20°16.8371' > -1216.8371' > -12168371 Jan 6, 2020 at 20:11
• I think it would be very useful if you publish this as an answer. Jan 6, 2020 at 20:28 