Plane Table Mapping

Plane Table Mapping

The power of trianglesAnd

Appropriate Technology

Any object can be located using triangular rays.

Virtually unchanged through history… except most of the guys now doing the horizontal measurements use a tape measure and wear pants (and don’t have wings)

Plane Table MappingSimple Equipment: a flat surface with paper attachedAn Alidade (a straight line sighting device)A pencil… this puts very accurate mapping in the hands of anyone

17th century onward….tool uses intersection of lines to locate points that are plotted on the paper on the table. Elevation is not considered in most plane table maps… only horizontal locations of objects on the landscape.

The process:Establish a baseline (the baseline needs to be scaled to the project and features that are to be mapped need to be visible from the baseline.Multiple baselines can be used as necessary… but the second baseline must be correctly tied to the initial baseline.The baseline can be extended to points plotted off the initial baseline…. Extremely large areas can be mapped with a fair degree of accuracy using this method

Process contd.The plane table is set up over the initial point on the baseline.Layout your paper so that it will easily contain the boundaries of the objects you are trying to map.You will need to calculate the scale… 1”=1meter? The scale will determine how much shows up on your completed map. The scale needs to be appropriate to the project!Use the Alidade (in our case triangular scale) to sight to the opposite end of the baseline.Draw in the baseline.

If you can see it… you can map it.Sight across the plane table at features that will be located on your map. One end of the Alidade will be on the initial point of the baseline, the other end will be exactly on the correct point, because light rays travel in straight lines…. And your eyes are highly accurate.MAKE SURE YOU ARE USING THE SAME EDGE OF THE RULER (Alidade) each time!

Your initial map…You are not mapping objects… yet.You are locating the points in space where objects are! You initial map will consist of nothing more than straight pencil lines (drawn in nice and light) with notes as to what sort of object you are locatingMAPPING is done by adding information to you locations…. Cartographic symbolism.

So why use the plane table?

“Unfortunately-or fortunately-the total station with data collection made the plane table and alidade into museum pieces”Is the plane table simply a museum piece? What can we learn from using these tools?Are there applications for this technology?