Preparing for the dig:

Before archaeologists can dig, a grid has to be set up over the site area so that we can accurately measure our units and the artifacts we find. The kind of grid we set up is called a Cartesian coordinate system. A point is chosen from which all measurements will be made. This is called a datum or origin.



A surveyors tool called a transit is then used to establish straight lines that run north-south and east-west intersecting at the datum. The north-south line will be our y axis while the east-west line will be our x axis. Since we are working in three dimensions, our z axis will be our depth below the ground surface. Wooden stakes are pounded into the ground along the north axes, usually at 10 meter intervals. The datum stake is assigned the coordinate N500E500 and all measurements are made from this point. A high number is chosen so that there will be no negative measurements. To determine the location of any point on the site, its distance from the datum in relation to the north and east axes is measured. If an artifact is found 27 meters to the north and 53 meters to the east of the datum, its coordinates are; N527E553. If an artifact is found 15 meters south and 33 meters west of the datum, its coordinates are N485E467. It seems complicated, but with practice, mapping on a grid system is pretty easy. Remember: add the numbers to 500 if you go north or east and subtract from 500 if you go south or west.