Greasby Benchmarks

Benchmarks indicate land height at points throughout Britain. They are set by Ordnance Survey and are used by architects and builders when planning new construction work. One of the main reasons is the prevention of flooding.

There are 23 properties in Greasby which have benchmarks, most are private houses. The few that can viewed in public areas are at -

Well Lane - on the garden wall of Halsall's Solicitors
126 Greasby Road - 'Oak'
154 Greasby Road - 'Salon 154'
213 Greasby Road - BP Service Station
Upton Bridge over Arrowe Brook (next to 12th Man pub)

The benchmarks are shown on Ordnance Survey maps. The figures displayed (feet on old maps, metres on modern maps) show the height of the benchmark line above Ordnance Datum Newlyn (ODN). Maps prior to 1921 showed heights to Ordnance Datum Liverpool (ODL). It took a few years until all newly published maps had moved from ODL to ODN and there are a few maps, mainly of the 1920s, which show benchmarks and spot heights to ODN but their contour lines are still to ODL. Locally, the difference between ODL and ODN is 3cm (1¼ inches) but in some parts it is much greater e.g. at Norfolk it is 46cm (18 inches).

Useful links -

Benchmark finder
https://www.ordnancesurvey.co.uk/benchmarks/

List of abbreviations
https://www.ordnancesurvey.co.uk/documents/resources/OSBM-list-abbreviations.pdf

History of Ordnance Survey and benchmarks
https://www.ordnancesurvey.co.uk/newsroom/blog/ordnance-datum-newlyn-100-years-old-today

Convert ODL to/from ODN (suggestion - use 'points', '5')
https://www.ordnancesurvey.co.uk/gps/legacy-control-information/liverpool-to-newlyn

Find a location using its grid reference or vice versa
https://gridreferencefinder.com/