Map reading
Marjorie Henry, Contributor

As the discussion on map-reading skills tested in the last examination continues, I would like to begin today's lesson by focusing on drawing a cross section. This is part (b) of the question and reads as follows:

Figure 1 (provided as an insert) is a grid for a cross section across the valley of the Rio Grande along Northing 67, between Eastings 03 and 06 at the same horizontal scale as the map. Using the map as a guide, sketch the cross section on the grid and insert and label the position of the river.

A cross section is like a cutting made in the relief of the land. It is useful in that it helps us to visualise the relief and allows for a better description and possible explanation of the landforms. To draw an accurate section across a contour map, follow these steps:

1. Draw a straight line between the two points for which the section is being done.

2. Take the straight edge of a piece of paper and lay it along the line drawn. Mark on it the points where the line crosses the contour. Record the heights of these points on the paper. Include also the points at which you begin and end.

3. On a graph paper, prepare a scale of heights using .5 cm to 50 m. Where there is no graph paper available, the horizontal lines are drawn at .5 cm apart on plain paper. Decide on the intervals, in terms of height, to be used on the vertical scale. Be guided by the intervals of the contour map you are using. Indicate the heights to the left of the graph paper.

4. Place the strip of paper on which you had marked off the points, along the base line of the scale. Transfer the points and their heights from the paper to the scale. Use a ruler to guide you by extending it from the paper with the points to the particular height on the vertical scale. Also, use a sharp-pointed pencil to indicate the points.

5. Having transferred the points and their heights from the strip of paper to the graph paper, join up the set of points. Where contours of the same height are crossed more than one time adjacent to each other, you will need to refer to the map to observe if the land between is higher or lower than the height of the contour.

6. Shade the land area of the section drawn. Indicate and label any outstanding feature, for example a road or river.

Vertical scale

In reference to the section of question 1 (b) given above, you would not be required to prepare a vertical scale for yourself since one was given to you. It simply means that you follow all the other steps outlined. I refer you again to the question and, in particular, the last sentence where it states: 'sketch the cross section on the grid'. Do not be misled by the use of the word 'sketch'. You are not being asked to do a sketch map but rather a cross section. Do not confuse them. Sketch is being used in this context to mean outline and this is what you do on the vertical scale once you have transferred the points from the paper on to the scale. As usual, aim at doing accurate work.

Section (c) of the question under discussion refers to a defined area of the map extract. Subsection (ii) requires that you:

List the THREE types of agricultural land use shown in the area.

Land use varies, but in this particular question you are asked to identify specifically agricultural land use. For this, you must refer to the key or legend of the map to identify this type of land use. Having done so, you need to ensure that these are on the section of the map given. Many of you will quickly record the various crops grown, for example, coconut and mixed or scattered cultivation. Please bear in mind that pasture is also agricultural land use. This is often overlooked.

A student at the Randolph Lopez School of Hope, Andre McTyson, creates an image of National Hero Marcus Garvey.