[Proj] Esri & EPSG Proj codes

[Irwin Scollar]

Melita Kennedy wrote in reply to my query concerning Esri proj codes:

>There currently is not a complete list available online. The 
>ArcObjects enumeration lists are not complete. These are definitions 
>defined by Esri. Sometimes EPSG adds the definitions later, and then 
>Esri updates the well-known IDs to the EPSG one (as more authoritative).

The Access database EPSG-v7_9.mdb contains 4924 COORD_REF_SYS 
codes.  4416 of these have Proj data which can be gleaned by 
combining the epsg and esri lists from the NAD directory out of a 
total of 6577 codes in these lists, eliminating "Unknown", 
"Unspecified" and searching for all correspondences between the NAD 
code numbers and the EPSG code numbers.

How were the esri and esri-extra lists in that directory obtained?

When EPSG adds definitions defined by Esri, do these get new numbers 
in the EPSG Access database or is there a systematic relationship 
between Esri numbers prior to adoption by EPSG and after 
incorporating them in the EPSG database?

Irwin Scollar