Computing, GIS and Archaeology in the UK

Just as we are settling down with the transition to open source, it would seem that a lot of other people are at least considering their options along the same lines, for whatever reason. This thread on the osgeo_discuss list, started off as a question about the value of open source to individual’s careers, but rapidly morphed into a discussion about replacing the ESRI packages. This seems to have lead to a general consensus about the areas where the open source packages do well and do badly.

The consensus seems to be that the open source packages are great for the behind-the-scenes and/or web-based work, assuming a relatively technically literate user, but that cartographic capabilities are sadly lacking at the moment. Furthermore, if you’re looking for one single replacement, then you’re out of luck- but you can assemble a toolkit that will get you all the capabilities you need, in a modular fashion. This does require a change in mindset- but it’s a lot more flexible and hopefully more powerful.

I hope that this recent upswell of interest and consensus about where the open source packages need improvement will help focus development in those areas. This does seem to be happening: this page is about plans for a cartographic library that can be shared amongst different packages. Sign up to show your support!

PS- if you’re in the UK you can still come along to our first UK OSGeo meetup at Stansted tomorrow (Thursday 1st) at 4.30. It’s free to attend, there will be some talks to start with (better finish writing mine), then we’ll sit down and try and figure out what we want a UK local chapter to do. There will be tea, coffee and biscuits too, so what are you waiting for!

Just what we needed- some good news- the AHRC are to continue funding the ADS. There isn’t any information publicly available yet as to how long the funding will last, and there is an intimation that charges for use will have to change, but all in all this is a good thing!

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!

Access 97 is still a popular choice for databases (especially in archaeology!) but the default ArcGIS 9.2 geodatabase is in Access 2000 format and cannot be opened in earlier versions of Microsoft Access. It is possible to create a geodatabase that can be used by both programmes.

1. Create a blank database in Microsoft Access 97 and save it to the location where you want your geodatabase to be stored. Close Access
2. In ArcCatalog, navigate to the database, and right-click to add a new object. Choose “table” rather than “feature class” or any of the other options.
3. Create a simple table called”test”, or similar- you can delete in in a minute. This creates all the geodatabase-specific tables that you need in the database.
4. Import your spatial data into the geodatabase, or create new data as required. You should now be able to access the data in both Microsoft Access and ArcGIS.

As always with geodatabases- do not delete geodatabase tables or feature classes in Access as they will remain visible in ArcCatalog. Only use ArcCatalog for deletions.