SW1A: 27 of 143 postcodes stand below a spring high tide

The ground at 27 of SW1A's 143 postcodes (19%) is lower than an ordinary spring high tide at London Bridge (3.9 m above Ordnance Datum).

• Ground at eight in ten of its postcodes: between 3.4 m and 15 m, measured from Ordnance Datum; the middle one stands at 6.0 m.
• 70 of 143 stand lower than the 1953 tide (5.41 m).
• 71 lie in the Environment Agency's Flood Zone 3 from the sea, mapped without defences.
• Mostly in Westminster; partly in Wandsworth.