For example: http://g.co/maps/2dpkj has the outline around the postcode area. I understand this is unavailable through the API , but where else can I get this data, eg in a KML format.
This is for UK Data
Most likely Google have a licensing agreement with Ordnance Survey that allows them to use the Code Points with Polygons data - I imagine they've then done some processing of the data to generate a KML file. Depending on your GIS skills and your ability to read the source file (ESRI/MapInfo), you should be able to do the same.
An alternative is to use the Code Point dataset, which has the virtue of being free and is supplied as a CSV file, however you'll need to re-process it to re-generate the polygons. There's a project on Google Code that I think will help you with this, geocoordconversion. Adrian Hills has a blog here on using the DLL with the Code Points dataset.
Is this what you're after?
https://www.google.com/fusiontables/data?docid=1jgWYtlqGSPzlIa-is8wl1cZkVIWEm_89rWUwqFU#rows:id=1
There are polygons for each postcode area, which was certainly good enough for my application.
Even if I don't know exactly where they got it from I would assume from the TIGER Data.
OK, so what TIGER is for the US is INSPIRE for Europe. INSPIRE claims all European countries to publish their spatial data. I think this directive is already in charge so you should checkout their portal and see if you find what you are looking for.
Here is a very useful API to do this now, create complex geo spatial queries(multiple postal districts,etc..)
UK Postal Code(ex. ZE1 0AE) ,Sector, District, City, and Wards Boundaries returns GeoJson, so you can integrate easily in google maps!
Simple monthly subscription model.. quick REST call :
/boundary/uk?postal-sector=ab16 9&postal-unit=ab16 9uw
Image of the results in GooleMap:
来源：https://stackoverflow.com/questions/9886500/how-did-google-get-the-outline-for-postcodes-on-maps