Surveying data: Lab group C

This week we built and attempted to use basic Roman surveying equipment. The groma, pictured above, has four arms arranged in a cross with weights hanging down from their ends, and from the center. By lining up three cords with a distant point (as Soren and Ruby are doing here), you can guarantee points in a line with the arm of your groma. This tool permits laying out straight lines and right angles. The other tools we used were cord, 7-foot poles, marking flags, and a measuring wheel.

Using these tools, we laid out three shapes during lab. First, we laid a square area, first 33×33 feet and then 66×66. In both cases, we first laid out two straight lines meeting in a right angle, then laid a third side of the box and measured it to the length of the first two. Having done that, we now had four corners. This took about 45 minutes.

Our second task was surveying a straight line (as if for a road). We found this much easier than the first task and managed to survey ~1,000 feet, as measured using google maps. Once again, we spent about 45 minutes on this.

Our final task was centuriate an open space by dividing it into 16 equal rectangles. We started this task by laying out an 88×88 foot square. We tried a new procedure this time; we measured two equally-long lines meeting in a right angle. Then, we sighted a point at a right angle from each corner to form our fourth corner. We thought that this method would be quicker and more accurate than measuring a third line. This turned out not to be the case; we re-measured this corner several times before the sides of our square were all equal. Then, we divided two sides into four equal parts using our measuring wheel and held cords perpendicularly across the square at these points. Where they met, we placed the corners of our smaller units.

We had a few persistent difficulties in using the groma. We wanted to be able to stick our groma into the ground so that it would be more stable, but our pvc construction did not have a point; the reconstructed groma we saw was sharpened. Also, our weighted cords swung too much. Perhaps heavier weights would have improved this problem.