UWO grad student out standing in her field.
In order to create maps of the archaeological sites we explore some mathematical conversion is required unless the map is being drawn by hand. With the advent of a number of good mapping tools available on personal computers, conversions from data recorded in the field to something acceptable to the mapping programs is required in almostall cases. This page will eventally provide a number of computer based tools to assist in computer mapping. The spreadsheet formats include an older version of Quattro Pro and SYLK so that they can be imported into the greatest number of product/versions (e.g Microsoft Excel, Lotus 1-2-3).
Cartesian Coordinates from Transit Readings
One of the most frequent tasks executed is to transpose transit recordings into cartesian coordinates which are required by most mapping programs. Given the frequency that this happens it is surprising that the software developers do not allow for direct transit input unless of course you have a transit that allows data to be recorded in magnetic format for computer use. Archaeological budgets being what they are these transits are usually not available. The attached spreadsheet will convert standard transit data (direction and the upper, middle and lower readings from the stadia rod) into Cartesian coordinates and calculate the relative elevation which would be required for a contour map. User instructions are included in the spreadsheet. The same calculations could also be used to plot a CSP where each location entered represented an artefact location. Depending on the sophistication of your mapping program you could substitute the elevation for a number representing the type of artefact and then plot concentrations of each type.
The preceding spreadsheet assumes that all readings are taken with the transit telescope at the level position. On hilly sites this is not always possible and it is also not productiveto keep moving the transit so you can read on the level. In this situation, in addition to the normal readings (horizontal angle, upper, middle and lower), you also record the vertical angle by which the telescope varies from the horizontal. For small vertical angles it makes only a very small difference to the Cartesian co-ordinates but does make a significant difference tothe elevation if you are drawing a contour map. The following spreadsheets allow you to enterthe vertical angle of the telescope and the Cartesian coordinates and elevation are calculated including this angle.
Cartesian Coordinates from Compass Readings
A less frequently used conversion is turning compass readings, a direction from each of two known points, into cartesian coordinates. To do this it is first necessary to establish two datum points with known coordinates. This can be done by measuring the distance between the two points and the direction of one from the other and then calculating their coordinates using the preceding method. Once this is complete, every point to be plotted is recorded by measuring the direction from both datum points and recording this in the field. This technique is useful for two dimensional maps but ismore limited than use of a transit since relative elevation data is not captured. The technique is useful for Stage 1 survey activity where it is necessary to record the relative locations of artefacts but carrying a transit along is prohibitive due to weight or manpower. One person can do a CSP using a compass.
Notes on How to Use a Compass
The following page contains a set of notes along with examples that were used to discuss archaeological mapping with a compass at a field school given at UWO in 1999. Methods described here could be used to create data that would be processed by the preceding spreadsheet.
GIS Scripts for Plotting CSP data and Spatial Analysis
This page contains the set of GIS scripts and associated documentation used in a paper published in KEWA 03-4/5. The scripts are used to plot data recorded during a CSP and conduct spatial analysis looking for non-random distributions of artefacts within the site. The scripts are for the GIS software MFWorks from Keigan Systems of London Ontario.
Future Additions to This Page
Watch for future additions to this page. Possibilities include the following.
Cartesian coordinates from two distance measurements.
GIS Scripts for MFWorks for common mapping jobs.
The mathematics behind the conversions.
A list of common mapping programs.
Other submissions are welcome. Please contact Jim Keronwith suggestions or submissions.