Stone circles of Cumbria
In the previous exercise you were presented with archaeological information in the form of a shapefile. Most archaeologists are in a position of having to deal with information which is in a completely different form, and perhaps more than one. You may have lists of site grid references in computer files (word-processor documents, spreadsheets, database files, text files), grid references published in print, or other digital formats such as CAD files. The last case is beyond the scope of this document, but the requirement to take lists of grid references and make them usable with OS digital data is a common one, and that is the subject of this section.
The file circles.txt contains the locations of stone circle sites in the county of Cumbria, some obtained from the county SMR, and others from the Megalithic Map website (http://www.megalith.ukf.net/). This is simply a text file, which could be created with any text editor (e.g. Notepad) or word processor (Word, Wordpad etc.), though in the latter case you would have to ensure that the file was saved in a text-only form. In this file each circle has been given an arbitrary number as an identifier, and this is followed by a grid reference. The names of the sites will be added later. A tab character separates the pieces of information on each line; commas could also have been used.
The grid references are in the form NY123456, which means that they refer to 100m squares. Unfortunately, these references can't be used directly in ArcView, because without the two-letter prefix they don't constitute unique locations (the numerical part of the reference recurs every 100Km), and ArcView can't make use of the letters themselves. The references have to be converted into distances in metres measured from the false origin of the Ordnance Survey grid. The Digimap Help facility supplies a useful explanation of how the Ordnance Survey grid is arranged, and two of its diagrams are reproduced here:
Looking at the figure 16, you can see a scheme of 500km squares, each identified by a letter; all the OS mapping fits within four of them, H, N, S, and T, and predominantly N and S. On the right is shown how the 500km squares are divided into the 100km squares used for giving grid references, each of these being identified by two letters. SV is the square at the extreme south-west of the mapped area, and its south-west corner is 0,0 in the OS grid. By counting the number of these 100km squares, it can be seen that the southern edge of the grid square NY is 500km (500,000m) north of the origin, and its western edge is 300km (300,000m) east. Therefore, all eastings co-ordinates within NY will be between 300,000m and 400,000m, while northings will be between 500,000m and 600,000m. For SD the figures are 300,000-400,000 (east) and 400,000-500,000 (north).
As an example, the grid reference NY215187 would equate to a location 321500m east and 518700m north of the grid origin. A figure has been added at the beginning of each part of the reference, and two zeroes at the end - this is logical if you recall that a six-figure reference identifies a 100m square, so that each corner-point is 100m from the next one. If the references had been four-figure, NY2118 would have become 321000, 518000. In performing this conversion it becomes very important to bear in mind the resolution of the original data. A four-figure reference NY2118, and the six-figure one NY210180 would both become 321000, 518000, despite the fact that they identify squares of 1000m and 100m sides respectively.
In the file circles2.txt some of the stone circle references have already been converted to a completely numerical form. Before you can proceed further you will have to add all the others in the same format. Notice that the first line of the file is different; this line contains the words which will be used as the names of fields in a table which ArcView will generate from your text file ('ID number', 'easting' and 'northing'). If you didn't include a line with these field names, ArcView would take the first line of data and use this instead, so that one of your sites would be lost.
It is important to keep the same identifying numbers as used in circles.txt, even though they are arbitrary, as they will be used later. When saving the file make sure that you keep the .txt file extension, even if you give the file a new name, as without it ArcView won't be able to access the file.
When you have completed the additions and saved the file, activate the ArcView Project window, click on the Tables option on the left, and click the Add button. A dialogue box will appear, but at this stage you won't see the name of your file because (as you can see by looking at the lower left of the window) by default ArcView is looking for database files with the .db extension. Change this to Delimited Text (*.txt), which will allow you to select your file. Another window will open showing the contents of the ArcView table which has been created (with the names from the first line of the file shown in highlighted fields). This table can be closed at this point; it doesn't have to be open for the next stage.
Open a new View, and add the theme cumbria.shp and coast.shp (the county boundary and coastline, taken from the Strategi data set). Now click on the View command in the menu bar and choose the option Add Event Theme. Another window opens, in which you can select any table which is part of the current Project (obviously this must be circles2.txt) and choose the fields which hold the x (i.e. easting) and y (northing) data; click OK.
Looking in the legend area of the View a new Theme will have appeared, called circles2.txt, and when you click the button to turn it on you will see a display of points something like this:
(assuming that all the co-ordinates you entered were correct!).
So far we have just a basic set of points with no attributes other than their
location. The next step will be to give them names.
The file names.txt contains the name of each stone circle, along with its ID number. This file should be made a table within the ArcView Project, just as was done with the file of co-ordinates (using Tables - Add in the Project window). When the Table window has appeared leave it open, and then open the tables circles2.txt again.
Click on the table names.txt to make it active, then click on the field name ID number, which will become highlighted. Now activate the circles2.txt table, and click on the same field name (ID number). It's important to do this in the correct order.
From the menu choose Table, then the option Join. The names.txt table will be closed, and its contents added to the table circles2.txt. This join is temporary, and can be undone with Table - Remove all joins. To make a permanent join, you can make a new shapefile (using Theme - Convert to shapefile as before), whose attribute table will contain the information from each of the tables which have been joined. Do this, and call the shapefile circles, adding it to the view.
You can make a more complete map by adding the shapefiles rivers.shp and lakes.shp, which have been extracted from Strategi tiles, and also add natpark.shp, the boundary of the Lake District National Park (this last shapefile comes originally from the Strategi data set, but has been processed using arc/Info to make a polygon from the original lines).
Although we have added only the names of the sites, it would be as simple to add any other attributes in exactly the same way - the number of stones, for example, or the dimensions of the circle. Much more sophisticated things can be done, of which just one example will be given.
It's often useful to be able to look at photographic images of sites along with relevant map data, and ArcView has facilities to enable you to do this, as long as the photographs in question are in digital form (bmp, gif and tif files are all acceptable, along with some others, though not the popular jpg format), either from a digital camera or scanned from prints or slides.
The first thing to do is to link a specific image to each point (in this case there is just one image, though, for the site of Castlerigg, in the file crig.tif), and this is done through the attribute table of the Theme in question. Follow these steps:
Fig. 18 ArcView toolbar
Fig. 19 Hotlink tool