Drawing a cross section
Marjorie Henry, Contributor

This week I will conclude the discussion on drawing a cross section. In reference to a map I gave, I listed for you the steps to do this in the last lesson. I hope you were able to follow them. Your section should be somewhat like this shown below.

The exercise does not end here for you must now complete the diagram properly. Here are the things that you must do:

1. Shade the land area of the section. You may use the side of the pencil point to do the shading, running it in the same direction throughout.

2. The vertical lines drawn at points A and B must be done in ink (preferably black ink).

3. Write the heights, that is the vertical scale, in ink.

4. Write a title. For this exercise it could be simply - SECTION

DRAWN FROM A TO B.

5. Identify outstanding features such as the valley and the spot heights. Draw an arrow where they occur and print the name of the feature.

This is illustrated below.

I must emphasise that you must do neat work at all times.

From the section drawn, you are able to identify the shape of the land, for example, where there is a steep slope or a gentle slope. You can also determine the intervisibility of points, that is, whether any two points on the ground are visible from each other. For example, in reference to the section done above, if you are in the valley, can you see any of the spot heights? To determine intervisibility, you begin by drawing a line from one point to another. If the line you have drawn passes through the land, then the points are not visible from each other. If, on the other hand, the line does not go through the land, then the points are visible from each other.

In the examination, the test on cross section can be done in one of the following ways:

(i) Drawing an entire section, however, you are usually given the frame in which to do it. The onus is on you to complete it properly as indicated above.

(ii) To complete a given section. For this, a part of the section is done in the frame.

(iii) A complete section can be given and you are then asked to label some features.

Please note that in each case you must refer to the given map, study it carefully and then identify the section given in the test. Accurate and neat work will ensure maximum marks for this exercise.

Use the map given last week and draw other sections for further practice, for example from P to Q and C to H.

Marjorie Henry is an independent contributor. Send questions and comments to kerry-ann.hepburn@gleanerjm.com