Reading a PRJ file

[John_RMellor__GISP]

I received a DWG file that had an attached PRJ file.  This is what the PRJ says; 

PROJCS["NAD_1983_2011_StatePlane_Illinois_West_FIPS_1202_Ft_US",GEOGCS["GCS_NAD_1983_2011",
DATUM["D_NAD_1983_2011",SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],
PARAMETER["False_Easting",2296583.333333333],PARAMETER["False_Northing",0.0],
PARAMETER["Central_Meridian",-90.16666666666667],PARAMETER["Scale_Factor",0.9999411764705882],
PARAMETER["Latitude_Of_Origin",36.66666666666666],UNIT["Foot_US",0.3048006096012192],AUTHORITY["ESRI",103038]]

My question is, at the end of the string it says - AUTHORITY["ESRI",103038], what does this mean? 

[Robert_LeClair]

Related to the AUTHORITY question, I found a FAQ for Authority: EPSG that talks about it a bit.  I can't find out what the 103038 means though.  Melita Kennedy‌ - do you know what the AUTHORITY["ESRI",103038] means?

[AdrianWelsh]

John,

This looks like a WKID or WKT which is a predefined coordinate system.

Coordinate Reference Systems‌

[John_RMellor__GISP]

I thought it looked like a WKID as well, but I couldn't find it either.  And I don't think that 103038 would match the front part of the PRJ; 

NAD_1983_2011_StatePlane_Illinois_West_FIPS_1202_Ft_US

Normally I wouldn't have the "2011" part and would be looking for 3436 or 102672. 

[MelitaKennedy · Accepted solution]

It's the original WKID Esri gave to this object when we added it. EPSG has since added it, so we did a "code change" to 6457. Either number will work if you give the number directly rather than use a WKT string. 

3436 is EPSG's number for NAD 1983 Illinois West (US Feet). 

I can't find 102672!

Melita

[John_RMellor__GISP]

Thank you Melita Kennedy‌.  Do you suppose that 102672 is an old code that was upgraded through a "code change"?  I found this link for 102672; https://epsg.io/102672 

I could find the EPSG 6457 online, but I couldn't find it in my CAD pick list. 

[MelitaKennedy]

Yes, you're right. It was NAD 1983 Illinois West (US Feet). I checked one location for it yesterday, and didn't check a 2nd one.

Melita