I have reviewed Getting polygon boundaries of City in JSON from Google Maps API? as well as the answers by german_martin and Kamil Latosinski. There are two critical weaknesses in Nominatim, using Malaysia as a case study:
1) The polygons include water (left = Nominatim, right = Google Maps)
Above are searches for 'Selangor'. I am aware that the boundary over water is the true administrative boundary, but for most visualisation exercises, this would make it look quite weird.
2) Postcode-level data is very coarse, at least for Msia (left = Nominatim, right = Google Maps)
Above are searches for '11900, Penang'. Nominatim just doesn't have it.
So, you can see why I really need to extract the JSON from Google Maps.
Does anyone know how to do this, preferably programatically so I can iterate over 2000 postcodes?
However, if it requires manual effort, I'm willing to do it.