Beckenham and Croydon sit two kilometres apart, on the same trains, in the same school catchments.
Now colour every postcode by what a square metre of home actually costs there.
Green means cheaper floor space. Croydon runs about a third under Beckenham, street for street.
That's over two hundred thousand pounds back on an average home.
Beckenham's cheaper twin is on this map. Find yours, free.