In message , John Salmon
writes

As a matter of interest, where did 'IG' come from? In my view, its
derivation is the least obvious of all the postcodes. I can work out
all the other slightly obscure ones e.g. SP=Salisbury Plain,
DG=Dumfries & Galloway etc., but the only suggestion I've ever heard
for IG is Ilford & Gants Hill, which seems unlikely.

I suspect that IG reflects the names of the first two post towns
within the postcode - Ilford (IG1 to IG6) and Chigwell (IG7).

Much the same happens with SM, where the first two post towns within
the postcode are Sutton (SM1 to SM3) and Morden (SM4).

Presumably IL was avoided because OCR equipment couldn't be relied
upon to read the letters accurately, especially when hand written.

Many of the 2-letter codes were in use before postcodes for labelling
mailbags, and generally these were reused for postcodes, probably
because the sorting office staff knew them by heart. As a student in
the 60s I worked on the Christmas post in Edinburgh, and the incoming
bags were marked EH. Outgoing codes that I remember include AB, IV and
DD, but I think Glasgow was GW although it became just G for postcodes.

I think postcodes were introduced long before anyone had any idea of
OCRing them. For a time, at the primary sort a series of blue
fluorescent dots were printed on the envelope and latterly dot-matrix
barcodes. Both of these were done by real people eyeballing the printed
or written postcodes, though OCR is certainly used now.

Peter

--
Peter Campbell Smith ~ London ~ pjcs00 (a) gmail.com