Chart Properties and Principles

Scale and the relationship between chart and earth distances.

Scale refers to the ratio between the distances:

• on a navigation chart and
• the corresponding distances on Earth.

It tells us how much the chart has been reduced compared to the actual size of the Earth.

It's like a shrunken version of the world!

Expressed as a formula:

Consider a navigation chart with a scale of:

1:100,000

If you measure a line on the chart that's 1 cm long, it would represent a distance of 100,000 cm on the Earth.

From then you can calculate 100,000 cm into 1000 metres. (100 cm = 1 metre)

From then you can calculate 1000 metres into 1 km. (1000 metres = 1 km)

Question:

1 cm on a VNC with a scale of 1:500,000 = how many kilometres on the earth?

1 cm on the chart = 500,000 cm on the earth

500,000 cm = 5000 m

5000 m = 5 km

Answer:

5 km

There are a number of methods used to describe chart scale. 

Graduated Scale Line

The graduated scale line is usually located at the bottom of the chart. 

Using a graduated scale line the distance between any two points on the chart can be measured and compared with the scale line.