Contour lines and Aerial Photographs

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 heigh value (in meters) on a topographic map
3. Trig. beacons - indicated by a triangle which shows its unique number and height above sea level up to one decimal of a meter

Trig beacon

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

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