Interesting article on the BBC website
The postcode search lets you see the impact on your local high street. It’s a bit of a blunt tool but Green Lanes seems to have fared pretty well when I compared it to my home town where 11% of retail was lost. The overall message seems to be that online trade has prospered at the expense of walk in spending whereas services that need to be accessed in person (eating out, beauty treatments and so on) have done quite well.
Yes the aggregation of 'streets near your chosen postcode' to give a 'shopping area' is somewhat loose (I tried it using the postcode for the picture illustrating the story - of Pembridge Rd, Notting Hill - and got shopping streets all the way to High Street Kensington) but it's a useful indicator.
Pedantic footnote - the colourful illustration in the story is around 10 years old, none of the shops shown exist today.