Plane-Tabling
Plane-Tabling
geodetic work involved in making a map of a locale using a plane table and an alidade. In plane-tabling, as distinct from other types of topographical surveying, the plotting of points on the plane table that correspond to characteristic points on the terrain is done graphically; the contours of land areas, rivers, lakes, roads, populated areas, and other elements of the terrain that are designated on the map by conventional symbols are drawn to a predetermined scale according to the points. In topographic plane-tabling, the topography of the area is also shown on the map by lines of equal elevation (horizontals), elevation markers, and conventional symbols.
The plane table is set up at point A on the terrain (see Figure 1) and oriented toward point B along line ab, which is set on the plane table. The alidade is used to draw lines AD and AC, connecting points D and C, on the plane table. A range finder is used to measure the distance to the points, and the line segments ad and ac are laid out on the plane table in the appropriate scale. If the angles of inclination of line segments AD and AC are measured, the relative elevations of points D and C may be determined, which makes it possible to show the topography of the terrain on the map. For plane-tabling of large areas, a geodetic reference network must be constructed and supplemented by points of a surveying network created by analytic methods (theodolite elevation and tachymetric traverses, as well as analytic networks and chains) or graphic methods (geometric network and plane-table traverse). The surveying of small areas (10-15 sq km for a scale of 1:5,000 and 2–4 sq km for a scale of 1:2,000) can be put on a single surveying network.
