There are numerous plans showing the features at Crickley Hill – some are simple pencil drawn plans (done in the field), but most have since been reproduced in ink, for both durability and to make features more visible. When I was digging at Crickley, I remember planning (drawing) contexts – this was done using a 1m grid that had been divided into 10 x 10 cm squares. Any item the size of a 2p piece or larger was drawn. This resulted in very detailed plans (anything smaller was unlikely to show up when the plan had been reduced to scale).
Digitising: what and why?
‘Digitising’ the plans means creating digital versions of the scaled down drawings – effectively tracing the plans in a special computer programme. This is done using either a tablet and special type of mouse with cross-hairs to trace the paper plans into the computer (which is what I did when I started this task in AutoCad), or an ordinary mouse to trace scanned plans from the computer desk-top (which is what I’m now doing in GIS).
There are many benefits to digitising plans – a more durable record is created (though as working with Crickley has shown, there are problems in anticipating what type of media may be used – or may survive – into the future). This record is very duplicated and modified, which means is can accurately be incorporated within publications, or shared in other ways.
A really useful aspect of digitised plans is the ability to rapidly show the distribution of finds in relation to context. By seeing where particular types of finds were used (and how many were used within particular contexts) we can begin to ask more searching social questions of the evidence. For instance, by looking at the distribution of particular finds (such as spindle-whorls), it may be possible to question the ways in which buildings were used, and even the way people worked together, considering social relationships and identities. This needs a drawing programme that can incorporate data from a database.
I first used (in 1997-99) a programme designed to incorporate data within drawings called G-Sys, along with AutoCad, but I no longer have this programme, as my copy stopped working with more recent operating systems a while ago. So when I returned to this task, I had to learn how to do things slightly differently, using the new GIS programmes commonly used for this job. I previously used a computer programmes called ArcMap in ArcView (part of ArcGis) to do this. However, as not all volunteers don’t yet have access to ArcMap – a very expensive programme – I also use QGis (an open source version).
Today’s job was to complete information and instructions for volunteers, showing how to use ArcMap, which I’ve just finished. I’ve just uploaded this file to a Google Groups page that I use to share documents with multiple volunteers:
I’ll very quickly run through what I’ve been doing in GIS. I’ve taken a plan of the 10m x 10m grid plan used during the excavations at Crickley, and coordinated this to the UK OSGB36 coordinate system, using easily recognisable reference points (for which I’ve obtained coordinates from an OS map):
I’ve then taken plans (the shown example is an interpretative plan that I’ve used for training purposes – this was created by a regular participant on the Crickley excavations: John Gale), and georeferenced these to the site grid and UK coordinates:
Having previously created and coordinated layers in which to digitise, I’ve then effectively traced around features using the mouse (here showing ArcMap):
This sometimes needs modification, to ensure accuracy (again showing ArcMap):
Here’s this building platform digitised in ArcMap:
I’ll go through this process, until I’ve digitised all of the features on a plan (here showing QGis):
This is an example of a digitised plan created in QGis:
GIS programmes can also be used to create large scale maps, showing the distribution and location of sites (this has been modified in Photoshop, by colouring the sea):
It’s been a long day, so I’m going to stop for now, and will continue tomorrow with posts 8: ‘Preparing to teach a Community Education workshop’ and 9. ‘Writing and publishing Academic and independent research’.