I have a dataset of traffic monitoring stations in Ohio, and I am trying to locate these stations in Lat/Long.

Here is an example:

example row of data

This station is located in Franklin county, along Interstate 71. CTL_BEGIN, per the Ohio Department of Transportation, is the "County True Log" Begin number. I am not sure of the reference point, but I would imagine it is a linear distance along this route from some reference point.

In the geometry field, one can see 7 digit coordinates (-9237663.3157 4859645.310999997). I tried entering these coordinates into a UTM -> Lat/Long converter, with UTM Zone 17, North Hemisphere, but this worked out to somewhere very much not in Ohio.

Here is a link to an admittedly sparse document on Ohio's coordinate systems, which I did not find helpful, but someone else may.

Any ideas how I would go about converting these coordinates, or otherwise locating these stations in Lat/Long, so that I may map them and do distance calculations with other coordinates?

Edit: For those who are operating with a Shape file and Python, if you import your .shp file into Geopandas, and then call .to_crs, you can convert quickly into the coordinate system of your choice. Calling .crs on your Geodataframe will tell you the system your data is using. I should have called that and I would have had my answer!


1 Answer 1


http://projfinder.com/ is a useful utility for finding the coordinate system of a set of points when the system isn't known.

If I put that point of yours in the X-Y boxes and go to Ohio, I can see a couple of possible locations around Columbus (and in the whole state there's some points way up north..)

enter image description here

The southernmost one appears to be on I71 at a junction:

enter image description here

(faint yellow circle, centre)

and this is EPSG:3857 which is the standard "Web Mercator" coordinate system. I'd wager that's what they are.

Coordinate convertors from EPSG:3857 to lat-long (EPSG:4326) or any other coordinate system are available via the PROJ library, with interfaces in Python, C, R, and a dozen other languages, or command line, or any GIS such as QGIS.

  • Fantastic, I had not heard of that tool before, and will definitely be using it in the future! You are correct, EPSG:3857 looks like the system being used. I tested some other points and they all match up to the correct roads. Much appreciate the help! Commented Apr 29, 2021 at 14:30

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