More on map reading
Marjorie Henry, Contributor

The focus in the last lesson was on grid reference, one of the skills tested in the map reading question of the last examination. At the end of the lesson, I gave you an exercise on this. I do trust that you took the time to do the exercise as it was intended to assist you to reinforce the concept. You were asked to give six-figure grid references for four points. Here are the answers:

Before I leave grid reference, I need to advise you of the following:

• There will be variation on the third and sixth digits when stating a six-figure grid reference for a point. If you applied the method suggested, that of using a bit of paper, extending it between the two adjacent grid lines, marking the points of the two lines on the paper, then using a ruler to divide that distance into 10 equal parts, you would have noticed that it was not always that one of those divisions fell exactly on the point or place for which you needed the grid reference. This was the case in the exercise given. You are allowed to use either digit in your answer.
  
  
• Whenever the point for which you are giving the grid reference is exactly on a grid line, then the third or sixth digit is zero. This was the case for the trig station K9. It was exactly on the northing 13.

Measuring distance was the next skill tested in the question under discussion.

Once you have identified the points between which the line is to be measured, that is, a road or railway, this can be done by using either a bit of thread (thin cord) or a bit of paper. If you choose to use a bit of paper, place it on the line. Mark off the starting point on the paper. With the help of a divider or a sharp pointed pencil, guide the paper along the line. Mark the paper at the point where the measurement must end. Extend the paper on the linear scale found at the end of the map, to find the distance. The thread or cord is used in the same way.

Here is the part of the question to test this skill:

• What is the length of the railway from its end on the coast near to Factory Pier (square 2411) to the point where it crosses the main road (square 2313)? Give your answer correct to the NEAREST 100 metres.

Follow the guidelines given to arrive at your answer. Note carefully that you are asked to give your answer to the NEAREST 100 metres. The map extract has linear scales done in miles, yards and kilometres. Make sure to select kilometres as instructed in the question. Extend the paper/cord/thread along the linear scale between the points marked. If you used paper, the distance would be 1 km 900m.

If you used cord or thread, the distance would be 2km. Either answer is correct. Here are two exercises for you. Refer to the same section of the map extract of Basseterre, St. Christopher, that was published with the lesson last week.

(i) What is the length of the main road from where it is joined by the secondary road in grid 2312, north easterly to where it cuts northing 14? Give your answer correct to the NEAREST 100 metres.

(ii) What is the length of the secondary road from where it is crossed by the railway (225129) northerly to the northing 14? Give your answer correct to the NEAREST mile.

Marjorie Henry is a vice-principal at Glenmuir High School and is head of the Geography Department. She teaches the subject at the CSEC Level.