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Rocky Mountain Ramblers Association

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A topographic map is a two dimensional representation of part of the earth's surface. Contour lines, colours, and shading are used to indicate elevation.

There are four pieces of information you need to know about a map before it can be of much use to you. These are:

  1. Scale,
  2. Orientation - which direction is North,
  3. Magnetic Declination - the difference in direction between true north and magnetic north, and
  4. Contour Interval.
Not all maps give you all this information. City street plans are particularly bad.


1. Scale of the Map

The Scale of a map tells you how many units of length on the ground are represented by 1 unit of length on the map. Without this information you do not know whether one centimeter on the map represents 1 kilometer, 2 kilometers, or 10 kilometers on the ground.

The topographic maps used for hiking in in the Rocky Mountains have a scale of 1:50,000, i.e. 1 cm on the map represents 50,000 cms ( or 1/2 km ) on the ground. There are also 1:250,000 maps which cover a larger area in less detail - these are useful for identifying mountains which are further away or for planning longer trips.

Some scales and their meanings:

ScaleMetric meaningImperial meaningComments
1:50,0002 cms to 1 km1.25 inches to 1 mileCanadian, British, and European maps
1:250,0001 cm to 2.5 kms1 inch to 4 milesCanadian and other maps - used to get overall view of area
1:63,3601 cm to 2/3 km1 inch to 1 mileOld British maps
1:62,5002 cms to 1.25 km1 inch to 1.04 milesUS topographic maps (15 minute series)
1:25,0004 cms to 1 km2.5 inches to 1 mileMore detailed maps (US, Canada, Britain, and Europe)
1:40,6802.5 cms to 1 km1 inch to 1 km!Some newer US maps

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2. Orientation of the Map

There should be some indication of which direction North is on the map. Many maps have grid lines criss-crossing the map. Normally these run North-South and East West. However this is not always the case. There is a 1:250,000 scale map of Jasper National Park that does not follow this norm.

Grid References

Grid lines are drawn on our 1:50,000 maps at 1 km intervals. A grid reference locates a position to the nearest 100 meters. However any 6 digit grid reference will also occur at points 100 km north, south, east and west of this point. So for a more precise reference always quote the map number or the full grid reference using the other numbers on the side of the map close to the corners.

map grid example The first 3 numbers are the west-east reference and the last 3 are the south-north reference, e.g.:
  • The grid reference of point x is 574138

  • Point x is 4/10ths of the way from the 57 line to the 58 line

  • Point x is 8/10ths of the way from the 13 line to the 14 line

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3. Magnetic Declination of the Map

There are 3 different Norths that we need to know about: The Magnetic Declination at a point on the earth's surface is the angle between grid north and magnetic north.

Somewhere on the border of most maps there is a set of arrows to indicate the relationship between the 3 norths at a particular point on the map. Usually, there will also be a narrative like:

Magnetic North was 20 degrees east of grid north in 1976 and this angle is decreasing by 5' a year. (1' means 1 minute or 1/60th of a degree. There are 360 degrees in a circle.)

Some examples of magnetic declination:

magnetic declination examples

Knowledge of the magnetic declination is needed in order to use the compass correctly to either find your way or identify distant mountains. Most maps and compasses have 360 degrees in the circle. However in Norway they use 400 degrees to the circle - so beware!

Taking Compass Bearings

From Map to Ground

This technique is used for finding out which way you want to go from a known point - used for navigation in treed areas and in bad visibility conditions above treeline.

From Ground to Map

This is used for:
  1. Identifying unknown objects or mountains from a known point or
  2. Finding your unknown position on the map from 2 or more known visible objects.
Instructions for (i) below:

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4. Contour Interval of the Map

A contour line is a (usually brown) line on a map joining points of equal altitude (height above mean sea level).

The contour interval is the distance vertically between the altitude each individual contour line represents. When reading a map, contour lines give you information on what the topography of the area is likely to be. The closer the contours the steeper the ground. By interpreting contour lines it is possible to imagine a 3 dimensional picture of what the ground might look like.

Some 1:50,000 scale maps of the Rocky Mountains have a contour interval of 100 feet; i.e. separate contour lines are drawn joining points of altitude 4000, 4100, 4200, 4300 etc feet above mean sea level. 1:250,000 maps of the area have a contour interval of 500 feet. Using a 100 foot interval on these maps of the Rockies would make them too cluttered. There are some 1:50,000 scale maps of the Rockies that have a 20 meter contour interval below 2000 meters and a 40 meter interval above 2000 meters - these can be very confusing. Others have a 50 meter contour interval. So it is important to check the contour interval on every map! However in Saskatchewan some 1:50,000 scale maps have a contour interval of 10 feet and 1:250,000 scale maps have a contour interval of 100 feet. This is necessary to show any variation of altitude there. In the mountainous areas of the US, contour intervals seem to be 80 feet on the 1:62500 scale maps and 40 feet on the 1:40680 scale and 200 feet on the 1:250,000 maps.

Understanding Contour Lines

At first glance all the wiggly brown lines on a map may seem meaningless but detailed study of them can reveal a lot about the landscape. With practice, from studying contour lines you will be able to form a 3-dimensional picture in your mind of what an area may look like. What about other shapes of contours that represent ridges and valleys? Which are the ridges and which are the valleys? The analysis is often made easier by there being a blue line representing a stream, and streams usually run in valleys. A good way to find out where the ridges and valleys are is to Draw a Section:

map section

One must realize that this is an approximation of the terrain. The following illustrates two equally valid interpretations of contours:

two valid interpretations

two valid interpretations

two valid interpretations

With continued study of topographic maps and contour lines you will be able to picture your hike from the map while sitting in your armchair. However that must not stop you getting out there and doing it!!

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