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I have data for Chicago, Illinois, that is in WGS84 CRS. I need to convert it to a metric projected CRS, and I've found several possible options:

  • EPSG 3528
  • EPSG 6454
  • EPSG 2790
  • EPSG 26971

Among these, 6454 seems to have the latest revision date. Other than that, how should I know which one is the "best"? I don't have any special requirements (or perhaps I don't know what I should look for...)

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As you already hint at in your question, there is really no "best" projection. What you use depends on the requirements of your project and how you want to display spatial data. That said, the most commonly used metric projected CRS for Chicago (and eastern Illinois more generally) are:

  • NAD83 UTM Zone 16N (EPSG 26916)
  • NAD83 StatePlane Illinois East FIPS 1201 (EPSG 26971)

A number of other projections will work as long as they are based on a modern datum like WGS84 or NAD83 (or updates thereof). I would definitely stay away from projections based on NAD27 though, as you can see fairly substantial data shifts (at least several meters) when reprojecting from NAD27 to more modern options.

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  • Thanks. What is the main difference between these two? Would it be correct to say that EPSG 26971 is more specific to Illinois and thus would be more accurate?
    – amitr
    Commented Jan 7, 2020 at 15:45
  • In theory, the state plane system has less distortion than the UTM system because it uses smaller zones. However, in practice this difference is basically negligible. I'd base my decision more on who you anticipate using the data. Illinois State Plane East is in common use within the state, but if others are going to access the data I might choose UTM simply because it's more widely used and people won't be surprised by it.
    – lambertj
    Commented Jan 7, 2020 at 15:57

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