When I was about fourteen-years old I made a papier–mâché volcano. It was ugly and bright: a behemoth of a model that couldn’t even do a bicarbonate soda and vinegar ‘eruption’. It did, however, have a little model of a skeleton at the foot of the mound, which I like to think helped me get my B grade.
Apart from that I had very little interest in geography – it just seemed to be about rivers and coastal defences. I’d like to think that had I better understood the importance of geography to archaeological research I would have paid more attention, but I honestly don’t even remember what fourteen-year-old Matt wanted to be. Probably not an international man of history, I suspect.
I begin with this largely irrelevant story as a means to moisten the rather dry subject matter that follows, but also to demonstrate how it is never too late to foster an interest in topography, geology, cartography and other such disciplines.
As it happens, mapping and spatial analysis has become a major aspect of my archaeological research and I have begun to fully appreciate the importance of the natural landscape to our understanding of past occupation.
Presenting and interrogating spatial data through maps is a pretty essential skill for the archaeologist, but training can be hard to come by and I have largely learnt how to do it through a handful of knowledgeable people and lots of trial and error.
To repay the kindness offered to me by such people I present the first of several (perhaps many) tutorials: how to make a simple map using ArcGIS.
Students and academics often use ArcGIS (currently version 10.2.2) because it’s really good and their university has a subscription to it. It is monstrously expensive to purchase for yourself, though, but don’t fret: I have heard good things about open-source (i.e. free) GIS packages like GRASS GIS and QGIS.
Before you can begin you will need a base map. Generally speaking, it is best to go with a raster dataset, and for topography I use Digital Terrain Models (DTM files).
In the UK you can access free mapping data from the Digimap service provided you are affiliated to a subscribing university. If you aren’t then you can get open-source data from sites such as ShareGeo Open, Geofabrik and OSGeo.
When you first load up ArcGIS the screen should look something like this:
On the left is where your datasets are managed, the centre is where the map is displayed and the right is where you can use some of the in-built features. The top bar follows the standard Windows model that I’m sure will feel familiar.
To add the base map you downloaded (or bought your professor drinks in order to obtain) click on the ‘Add data’ button:
You can change the way the map is visualised by double clicking on the dataset in the left-hand column (in this case ‘uk’). Under the ‘Symbology’ heading you can change how the map is displayed as so:
Pro tip: if the resolution of your dataset is good I’d recommend enabling ‘use hillshade effect’ for an even sexier map.
Now we need to prepare some data points to upload to the map. This can be a bit tricky to get your head around, and there isn’t really time to explain the underlying concepts in a blog post, so I’ll just crack on.
Normally archaeological site reports give the coordinates for the location of the site. For example, the report for the ‘great hall complex’ at Cowdery’s Down, Hampshire gives its reference as SU 657 532.
GIS programs like ArcGIS work best with x/y coordinates though so we can use websites like UK Grid Reference Finder to help us convert them. You can also use the Batch Convert Tool to convert multiple data points.
Open a new Excel spreadsheet and input your data points like so. Note that less is more with regard to formatting– ArcGIS is quite finicky – so avoid fancy fonts and colours.
To the left of the screen you should now have a new addition. Right click it and select ‘Display XY Data’. Make sure the correct ‘X Field’ and ‘Y Field’ are properly selected and press ‘OK’. If it tells you about a specific Object-ID Field just press ‘OK’ and it will go away (like charity sales people).
That’s all for now (it’s very sunny outside) but I’ll cover more stuff in a future post. If you’re really keen, though, try experimenting with the zoom feature and have a think about how the topography of the region might have influenced the positioning of the site.