Indexkontur

Indexkontur, often translated as index contour, is a contour line on topographic maps that is drawn darker and labeled with its elevation. It marks a larger elevation interval than the surrounding lines and provides a quick reference for the terrain. Typical maps place index contours at regular elevation steps, for example every fifth or tenth contour line, depending on scale and terrain, with the elevation value printed on or beside the line. Between index contours lie auxiliary contours with smaller intervals to depict finer relief.

The primary purpose is legibility: bold index contours help readers gauge altitude and gradient rapidly, aiding navigation, planning, and geomorphological interpretation. They also serve as convenient anchors for grid or coordinate references on the map.

In map production, index contours are derived from digital elevation models or from traditional surveying and photogrammetry. In digital cartography, GIS can generate multiple contour sets and highlight the index ones through styling or labeling rules.

The choice of contour and index intervals depends on scale, elevation range, and intended use. In mountainous terrain, index contours may appear more frequently to maintain readability; in flat areas, they may occur less often.

Indexkontur is a standard concept in topographic cartography and GIS, used on both physical maps and digital products to convey three-dimensional information on a two-dimensional plane.