Ordnance Survey Bench Marks

The conventional logic when it comes to appreciating the built environment around us is that we should all be looking up more. It’s so easy to miss Regency or Art Deco details above local shops after all. But looking down has its benefits too.

Pavements and low walls are full of interesting features including old street signs, boundary plaques and coal chute covers. The letters ‘FH’ and ‘H’ on walls and small posts denote fire hydrants. ‘HCS’ and ‘HC’ cut into granite kerbstones once indicated hackney carriage stops. Much more subtle though is a series of small symbols that consist of a horizontal line with an arrow pointing towards it from below. They are Ordnance Survey bench marks.

One example is that on the front wall of 56 New Church Road in Hove. It was carved into the yellow brick many years ago. Another sits below a crown on an iron post in front of the Withdean Grange telephone exchange on Preston Road in Brighton. Others exist, according to Ordnance Survey’s database, on Harrington Road, Preston Drove, Balfour Road, Lowther Road and Beaconsfield Villas nearby. They are certainly not rare.

The network of symbols was put in place as a reference frame for heights above Ordnance Datum (mean sea level). Numbers on corresponding maps give heights at each point. Although the network is no longer maintained, around 500,000 of these so-called ‘lower order’ bench marks still exist. They are being destroyed though when, for example, walls are demolished or pavements are widened.

Ordnance Survey’s list states that the bench mark on New Church Road is a cut mark at 0.7m above the ground and 12.067m above mean sea level (presumably different to that of today). Now that I know what these curious symbols mean, I spot them all the time.

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