CTC Navigation Bootcamp 2017 - Module 4 - Contours and Topomaps

Tuesday, April 11, 2017
Yo Navigators!

Now that we familiarized ourselves with navigating in the plains let's add the third dimension - altitude or elevation. Time to head out for the hills now. 
Before we start climbing up the mountains let us get familiar with contour lines, elevation profiles and topographic maps.

Module 4

Type: home assignment
Date: Tue Apr 11th
Deadline: Sun Apr 16th
Duration: 1-2 hours
Submit one set of answers per team
All team members to participate & understand

Contour Lines

To get into the third dimension (elevation or altitude) : up in the hills we should familiarize ourselves with topographic maps (shortly: topomaps, also called terrain maps in Google)
A topomap will use contour lines to indicate the relief of the area on the map which will allow us to identify valleys, peaks, ridges and other terrain features to plan our trekking trails in mountains
A contour line joins points of equal elevation. A contour line typically circles around a hill and if you would walk along the contour line you would be proceeding horizontally
Each contour line on a topomap will indicate an increase or decrease in altitude (say. 20 meter steps)

Consider the hill below for example: we have broken it down in steps of 20 meters altitude gain.
Below the hill you can see the contour lines projected as they would represent the hill on a flat 2-dimensional topographic map:
The innermost contour line is the peak of the hill

One important observation is that the Eastern (right) slope of the hill is less steep (contour lines are spaced wider means slower increase in altitude)
While the Western (left) side is more steep - the same can be observed from the contour lines which are very close to each other indicating a faster increase in altitude as we climb the hill from that side

Topographic Map

Now let's take a look at a couple of real hills near the city in Google Terrain maps
Open maps.google.com in your browser and Getting Around choose "Terrain" which corresponds to topomap
Now search for following hill near Chengalpattu: 12°40'47.6"N 79°58'00.6"E (just type in this latitude, longitude)
If you don't see contour lines immediately then zoom out a little with your mouse until they appear:

The map shows a few hills immediately West of Chengalpattu town, East of the Palar river
Thicker lines indicate 100m contour lines, finer lines show 20m contour lines
The tallest hill is 200m high with steep (closesly spaced contours) slopes on West, North and East and a more gradual (wider spaced contours) slope from the Southern side
The hill is surrounded by 4 smaller hills: a 120m hill West, a 120 high hill North, a 120m high hill Southeast and a 140m hill South
The innermost contour line for each hill corresponds to the peak of that hill. That contour indicates the overall height of the hill
Carefully look at the map and ensure you can identify all hills and their altitude

The easiest way to climb the center hill would be from the South where the contour lines are spaced more widely (means less steep) - orange line below

Ridges & Valleys

In addition to spacing between contour lines indicating the steepness of the terrain there is another important aspect: shape of contour lines.
Observe that the 140m South hill is round shaped (symmetrical) at all sides indicated by its circular contour lines
The Center hill is round at its North end (circular contours) while it's more prolonged stretched at its South end (U-shaped contour lines)
A continuous set of U-shaped contour lines (from lower to higher altitude) is called a "ridge". A ridge is a preferred candidate for climbing a peak from its base.
I have indicated 3 small ridges in the map below with orange lines (arrows showing base to top).

The opposite of a ridge is a valley which can be spotted by a series of inverted-U shaped contour lines (from lower to higher contour lines)
I have indicated four small valleys in the map below with blue lines (arrows showing base to top)
Carefully look at the contour lines of the above map and ensure you can see the ridge and valleys through the U or inverted-U shape of the contours


Wow... wow....wow... STOP Peter! ENOUGH theory for one session. Our brain is smoking! TIME for some hands-on now to grasp what we learned!

Assignment: try it yourself

Open Google Maps (Terrain view) and search for "Kannamangalam Forest". Zoom out a little bit until you see the contour lines

Take a screenshot of the map and (similar to the above example):
  • identify several peaks and indicate their altitude
  • trace a couple of ridges (orange colored lines)
  • trace a couple of valleys (blue colored lines)
Upload your resulting image in a public online album and share the link in this answer form.

Good luck - understanding contours is essential to become a navigator in the hills !



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