PLANE TABLE MAPPING PROJECTS IN FIELD GEOLOGY COURSES: INTEGRATING NEW AND OLD TECHNOLOGY

Currently the Plane Table mapping project has become somewhat of a “lost art” in undergraduate Field Geology courses, with relatively few departments incorporating a plane table component. There are several reasons for this: Alidade technology is obsolete compared to current surveying instruments such as a total station (TS), and the cost of survey instruments (old or new technology) is relatively high compared to other geological field equipment. Therefore, obsolete or inoperable instruments tend to not be replaced. We believe that the plane table project should be an integral part of the Field Geology course content. Plane table projects are where students learn to map at large scale (e.g. 1:120), and to create topographic maps with 1 foot (or less) contour intervals. This is an extremely valuable skill for geoscientists that specialize in hydrogeology, environmental, and engineering geology subdisciplines because many sites that have associated legal issues must be mapped at a large scale. Accurate topographic surveys are critical to modeling hydrologic properties.

Our approach to offering a large scale (1:120) plane table project was to combine the new with the old. The University of South Alabama summer 2002 field course used 2 traditional alidade instruments combined with a Sokkia SET500 TS. The mapping area consisted of a 100m x 70m exposure of Precambrian gneiss cut by granite dikes. 3 groups of 4 students were assigned the task of mapping the geology and topography at 1:120 using a 1 foot contour interval. The TS was rotated to a different group each day during the project, with TS groups averaging 120 data points versus 25 for alidade groups. To integrate data students downloaded the total station data to spreadsheets and plotted data onto the plane table, which was gridded to match the TS coordinate system. Rotating the TS allowed each group to collect twice the data compared to previous courses. We prefer the rotating system because the alidade forces students to understand fundamental principles, whereas the TS allows them to experience the efficiency of more advanced technology.