Wednesday, 11 November 2009

Benchmarks - the return of

As regular readers will know I tend not to use this blog as a vehicle for emapsite related happenings and offerings and to a broad extent this post continues this approach.

However, as someone who almost ended up a surveyor - it is thanks to UCL for putting me on hilltops in Wales and the subsequent opportunity to look through a theodolite for 6 months in the desert that brought me to my senses - I have something of a paleotard fondness for related features in our landscape, notably Trig Points and benchmarks.

I am equally aware that the arrival of GPS signalled the ultimate demise of such man made features; we simply don't need them. Try telling that to the legions of surveyors, chartered, engineering or other, who it seems from the flurry of requests, enquiries and complaints we have received, following the withdrawal of benchmarks from OS MasterMap, expect to see benchmarks on their mapping.

It would, indeed is, easy to make the case for ignoring them - benchmarks are not maintained and in fact most have had little consideration for more than 30 years, the site has been redeveloped or a road widened, the physical site has eroded, they are sometimes deliberately moved, ground heaves or collapses etc. In other words they (there are around 500,000) simply can't be trusted any more.

Benchmarks and trig points do seem to have a hold though on the psyche of those that ostensibly have no use for them - part luddite perhaps, part emotional symbol of a technocratic past perhaps, hard to tell.

Benchmarks (BMs) are the survey marks made by Ordnance Survey to record height above Ordnance Datum. BMs are usually found on buildings and other typically man-made features. They take the form Benchmark image on the ground with similar cartographic representation; strangely the recorded height had to be purchased from OS but is recorded on many maps too.

Most benchamrks that we see still are lower order benchmarks derived from an original network of nearly 200 Fundamental Benchmarks to create a physical manifestation of our national height system, the Newlyn Daturm (or Ordnance Datum Newlyn).

Various organisations ioncluding the RICS have published guidance on how to adapt to the GPS world, for example the Virtually Level guide is the latest in a new series from the RICS Geomatics Mapping and Positioning Practice Panel (MAPPP).

Being a smart business these are not of course removed from the database just tagged appropriately and it is a simple matter to reinsert them into the various products and services that we offer. After much discussion and muttering about how their reinstatement presents risks to those who would utilise them it was decided that we would reflect customer demand both from the professional community (who should be educated as to their lack of utility) and to the broader consumer market seeking information about their communities.

So there it is and there they are - enjoy, get steamed up, find your local one....

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