Friday, 27 February 2015

What's the point (on the map)?

In a previous post, we talked about the value of geo-locating some of the 20,000 or so fossil specimens we have processed in the 3D Fossils database. In this post, I want to explain a little more why it is useful, and also how we do it.

Visitors to the 3D Fossils site can at the moment choose to search by a number of criteria, for example, if I search for fossils from the Carboniferous I will return specimens around 300-360 million years old. However if I search for “Lyme Regis” I will only get those specimens where the location field contains at least those words. I won't see specimens from Charmouth, or Pinhay, both only a couple of miles away. At the moment, our system is not aware of any geospatial relations between the text in the locality field.

To fix this, we need to know where all our places are on the British National Grid. In the modern world where even your mobile phone knows exactly where it is within just a few metres, it is easy to forget that it was not always this easy :

  • A lot of our specimens were collected before the grid was standardised to the OSGB 1936 format currently in place
  • Distances were measured in miles or yards (sometimes even furlongs, rods and chains), rather than metres and kilometres.
  • Many of the localities are recorded in the style “small quarry (disused) on south side of lane, around 250 yards east of Dog and Duck public house, name of small village, etc”
  • There are plenty of places in the UK which share the same name, but are in completely different places. Examples might include Gillingham, Kent/Gillingham, Dorset, or Rainham, Kent/Rainham, Essex.
  • If two places sharing the same name is not confusing enough, some places like to move around. Dudley, in the two hundred or so years since it was recognised as a source of prime geological material, has been part of Worcestershire, Staffordshire and the West Midlands.
  • Sometimes, fossil dealers would not be keen to disclose the sources of their stock for fear of losing out on a sale. Hence we often see wonderful fossils with only scant location information, for example “Whitby” or “Lyme Regis”
Finally, sometimes the locality information can be so precise that there might be a risk of exposing the exact location of sites that may be on private land. In this case we obfuscate the locality slightly, whilst retaining full details on file should they ever be required for bona fide research.

Despite these challenges, we can use our resources to make our best estimate of the right place on the map, and we are being helped by a number of volunteers who can carry out a few minutes of investigation work for each one. Some of the resources we like to use are:

Ordnance Survey maps, old and new. We are lucky to have a comprehensive back catalogue of these, and in digital format too. We use GIS packages such as ArcGIS to examine them.
Geological maps, usually based on an OS map underneath, but the geology listed in the specimen data might be a valuable extra clue. You can have a look at some of our maps using the new Maps Portal
Gazeteers (such as the OS Open Data 50k version, or GeoNames, a crowdsourced alternative). These are simply lists of place names and their grid references. They can be very useful to simply get you to the right area to start looking, or where the locality information is so vague that there is no way to get any more accuracy. 
Web searches – sometimes old quarries will have become SSSI or RIGS sites and accompanying paperwork on these will often yield a grid reference. Similarly the original published descriptions of the specimens may provide location details
Friends and colleagues – sometimes, if a description is particularly ambiguous, contains colloquial references, or is spelled incorrectly, no amount of web searching will help. However, someone who is familiar with the area might instantly say “I know exactly where that is”!

When we find a point that we believe represents as accurately as possible where the fossil was found, it is just a matter of reading off a 12 digit reference (which represents the position, in metres, east and north of a datum point off the Isles of Scilly). We are compiling all these points into a database, which we can use to quality check the final results. I'll explain how we do that in a future post. 

We are a little more than half way through a list of around 4,000 points from the 3d Fossils database, but if you think this sounds like an interesting task then there are plenty more parts of our collection that would benefit from the same treatment. You can volunteer from home too, but if you're ever near Keyworth we'd be happy to show you around. Contact in the first instance. 

Simon Harris
GB\3D Team

No comments:

Post a Comment