The Earth
The Solar System & Time
Using Aeronautical Charts
Basics of Navigation
Distance, Speed & Time
Vertical Navigation
Fuel Planning
Practical Navigation Techniques
Radio Navigation
Practice Exam

Terrain & Obstacles

Contour Lines

Contours are lines on the chart that join points of equal elevation. The closer together the contour lines are, the steeper the ground is.

By mapping the ground like this, the contour lines show the shape of the ground.

This is an illustration of how contour lines and tinting (with some clever shading) can depict the elevation of the terrain.

The vertical elevation (increase or decrease in terrain height) between each contour line is written in the chart legend.

For our 1:500 000 Aeronautical Chart, the contour interval is 500 feet. This means a new contour line will be drawn whenever the terrain elevation increases or decreases by 500 feet above mean sea level (AMSL).


Similar to the image at the top of this page, brown tinting is used on the 1:500 000 aeronautical charts to make changes in elevation easier to see.

The chart legend shows the various shades of brown used on the chart. Darker colours are higher elevation and lighter colours are lower elevation. White areas (no tinting) have an elevation below 500 feet AMSL.

If you use a different chart, make sure to check the legend for any differences!

This image shows how contour lines and tinting are used on the 1:500 000 aeronautical chart


Obstacles greater than 300 feet above ground level are marked on the chart. This means there may be obstacles of 299 feet anywhere on the chart that are not marked.

There are various symbols used to depict obstacles on the chart depending on their height and whether the obstacle has light(s) on it. Next to the obstacle symbol is both the altitude and height of the obstacle:

The obstacle’s altitude (above mean sea level) in feet is written in bold
The obstacle’s height (above ground level) in feet is written in brackets

Spot Heights

Spot heights are marked on the chart to show the exact elevation of various terrain high points. There are two types:

Spot heights marked as a black dot with the elevation in feet written alongside
Spot heights marked as a black dot with the elevation written inside a white box show the highest elevation on that particular chart

Since obstacles are only marked on the chart when they are above 300ft, we have to assume that any spot height could have a 300ft unmarked obstacle on top of it. So if the highest spot height is 2300ft, you should add 300ft and use 2600ft as your enroute obstacle height.

Snowdonia is marked with 3560 in a white box as it is the highest elevation on the UK Southern England & Wales 1:500 000 chart.

Maximum Elevation Figure (MEF)

The lines of latitude and longitude are marked on the 1:500 000 aeronautical charts every half-degree (0.5°), which forms a grid across the chart. A Maximum Elevation Figure (MEF) is marked within each grid section, which shows the elevation of the highest obstruction in that area.

The MEFs account for the possible unmarked 299 foot obstacles. So in this image, the MEF of 2500 may be because of 2140ft terrain, which has been rounded up to 2200ft and had the 300ft added.