Heights and contour lines

Heights can be indicated in FOUR ways on a topographic map.

1.     Contour lines - lines (brown) joining areas with the same height above sea level. The contour interval (difference between contour lines) on a 1:50 000 topographic map is 20m.

2.     Spot heights - indicated by a black dot and height value (in meters above sea level) of a specific point on a topographic map.

3.     Trig. beacons (triangulation station or trigonometrical point) - indicated by a triangle which shows its unique number and height above sea level up to one decimal of a meter.

A Trig. beacon

4.     Bench marks - indicated by an arrow pointing to a main road with the height in meters above sea level.

Aerial Photographs

Aerial photographs are photos taken from light airplanes. These photos contain more detail e.g. orthophoto maps. Because it shows more detail the scale will be a large scale in comparison to a topographic map with less detail (small scale).

Three kinds of aerial photographs can be found –

• Vertical photographs
• Horizontal photographs
• Oblique photographs

Mapwork slide

Mapwork calculations from fenslin