Contour Lines

Contour Lines

Contour lines allow you to visualise from a map the slope and undulation of the ground

(©Crown copyright and database rights Ordnance Survey licence number 100054073 2013)

Contour Lines 

Contours



Contour lines are shown on maps in orange, connect points of equal elevation and are a means by which you can understand the shape (topography) and height of the land. Understanding contours is a skill that will allow you to look at a map and picture the hill, with depressions for streams/burns etc, hillocks and thin mountain ridges etc. Contour lines are pictoral, in that they do not exist on the ground.

Heights on maps are measured from sea level, and such heights have been calculated by Ordnance Survey by use of triangulation points (or trig points) or more recently by air surveys. You can tell whether a spot height has been land or air calculated by the colour of the text, with black being from land surveys and orange from air surveys.

Contour lines are normally shown for every 10 metres elevation, with a few exceptions. The height in metres is shown at various intervals on the map, but it would be impractical to show a value for each line, so instead, every 50m or 100m there is an index contour, which allows you to count up or down to calculate height of other lines.


Videos

Take a look at this video, which explains contours.




Examples 

   
    ©Crown copyright and database rights Ordnance Survey licence number 100054073 2013


Relating 3D to Contours

The following picture and associated map should help you to visualise how the 3D landscape is related to a 2D map, and the contours on it.

    
   The view from the side of Great Sca Fell in the Lake District - looking towards Meal Fell & Great Cockup


The Map of the Photo


    
    ©Crown copyright and database rights Ordnance Survey licence number 100054073 2013


Ordnance Survey Video

Another from Ordnance Survey, which is more specific to UK Maps




Map Reading Guides

Ordnance Survey have put together an interactive guide relating to Contours and Relief 


Also published are two map reading guides, the first one of which has good countour information included.