Computing, GIS and Archaeology in the UK

Vector One points us to an article in the Independent about how google are destroying Britain’s culture by not showing it on their maps. The interviewee, from the British Cartographic Society, is slightly hysterical about this- let’s face it google are not *that* evil, but I have to say I agree with the basic premise, and disagree with Vector One’s analysis.

The fact is that Google maps are not as rich and interesting as those the Ordnance Survey produces. I’ve said in the past that there is more to maps than simply directions from A to B. As more people rely on google and satnav for their map use, they will miss out on all the unexpectedly interesting things you might find whilst on the the way to B.

Vector One seems to be suggesting that this is more to do with people’s inability to read maps than the increasing ubiquity of digital alternatives. This, therefore, must be the fault of the UK government education policy. While this might be true to an extent, it’s a symptom rather than a cause in my opinion. Personally, I think the fault lies with the Ordnance Survey, they’ve missed a trick really. They could have produced their own widely available digital mapping eons ago rather than wrapping it in prohibitive licensing terms and restrictive interfaces. Given a choice of google’s over-simplified view of the world, or the rich detail of the Ordnance Survey in your satnav or digital device, maybe a lot more people would choose the OS.

A couple of people have remarked to me that one reason that they are not prepared to make the open source jump is the lack of support.

Well, last week I wrote about a mastermap importer that I had found. I said I would like to be able to merge the huge numbers of shapefiles produced into more manageable chunks. I got a lot of good advice as to ways I might be able to do that using gdal, which is really handy, BUT I also emailed the developer about the same problem. Two days later he released a new version of the software with that functionality built in.

To me, this highlights one of the big advantages of open source. People want to make their software better, and are willing to listen to suggestions. Small firms or one-man bands don’t have the inertia of the major firms and can respond to requests quickly and easily. To the user, that means flexibility and control. In other industries, that would be seen as an advantage, not a disadvantage, so why not in software?

I had some interest in the Access module for converting Ordnance Survey NGRs to Eastings and Northings (and vice versa) so I thought I’d risk putting the database on the site for download. It’s in Access 97 but should translate up to newer versions without much trouble.

I should also add that several people commented last week about an online NGR converter that looks really handy, and this excel spreadsheet full of handy vba functions for conversion offline.

Obviously this database is offered with no warranty: it has been scanned for viruses but I won’t be responsible for any damage done to you, your computer, pets, family, work colleagues, friends etc whilst using it. Other than that, you can share it, alter it or otherwise hack it to pieces. A little linkage back to here would be appreciated if it’s useful though!

Where is it? Here

After last week’s post I was asked in the comments to explain how to convert British Ordnance Survey Grid Squares to sensible Eastings and Northings, for use in a GIS. So here goes…

Firstly- to quote from the Ordnance Survey website:

The National Grid, like its military predecessors, consists of a systematic breakdown of the Grid area into progressively smaller squares identified first by letters and then numbers. The largest unit of the grid is 500km squares each designated by a prefix letter alphabetically from A-Z omitting I - the first letter to be quoted in today’s National Grid Reference. Great Britain is covered only by four of these squares - H, N, S and T. The 500km squares are then further broken down in to twenty-five 100km squares which are identified by a letter, again A - Z omitting I ( the second letter quoted in a reference).
On Ordnance Survey maps these squares are divided into smaller squares by grid lines representing 10 km spacing each numbered 0 - 9, from the South West Corner in an Easterly and Northerly direction.

The upshot of this is that there is a grid of 7×13 100KM squares superimposed over England, Scotland and Wales (Ireland has it’s own grid), each of which can be referenced either by two letters, or two numbers (counting from left to right, bottom to top, starting with 0). Traditionally, grid references in the UK have the two letter code, then the grid reference, eg SD 481 616 is the grid reference of my house.

To use these references in a GIS, ie to display point data by easting and northing coordinates do the following:

1. Find out the numbers representing the grid letters (SD is 3,4),
2. The column number is prefixed in front of the easting (eg 3481),
3. The row number is prefixed in front of the northing (eg 4616),
4. Add enough zeroes to have 6 digits in both the easting and the northing (348100 461600) *,
5. The number of zeroes tells you how accurate the reference is- the above reference is accurate to 100m.

* The far North of Scotland has 7 digits in the northing

Ah, but how do you know the numbers to represent each grid square? Well, there are complicated formulae for it but I find it easiest to print out this map and number the squares up starting with 0,0 in the bottom left corner.

It is possible to find php modules online to do this automatically for a web site, and I also created a visual basic module to do this in microsoft access. I won’t post the module as my web host will probably think it’s spyware or a virus, but feel free to contact me in the comments if you’d like it.

Hope this helps!