5. Distance There are two ways to calculate the distance between two places on a map. 1. Straight line method. 2. Curved line method.
1. To measure straight line distance (as the crow flies) between two points:
(a) Place the edge of a piece of paper on the two points on the map.
(b) With a pencil make a mark on the paper’s edge where it touches the two points.
(c) Place the marked paper edge along a linear scale bar and read the distance.
1 KILOMETRES012 3 Answer = 2.7 km
Fig. 13 How to get the straight line distance from Cronalaght to Carntreena in County Donegal
(d) Using the scale bar, count the number of full kilometres to the right of the 0 mark.
(e) Place any remaining measurement to the left of the 0 mark to get the tenths of the kilometre for an exact distance.
Short cut: If the map is 1:50,000 in scale, use a ruler to measure the distance between the 2 points in centimetres and divide by 2. This will give the answer in kilometres.
A B
2. To measure curved line distance between two points:
A B C
This usually involves measuring roads, rivers or coastlines. In order to measure a curved line distance, break the distance into a series of small straight sections which you will mark on the edge of a strip of paper.
(a) Find your starting and finishing points on the map. A B C D
(b) Place the edge of a strip of paper on the starting point on your map. Mark the paper at this point. Line up the edge of the paper with the road or rail line to be measured.
(c) Make another mark on the paper and map where the road line moves away from (or under) the paper.
(d) Keeping the marks you made on the map and paper together, turn the paper to meet the road underneath and mark the next section of straight line.
(e) Repeat the procedure until you reach the end of the distance to be measured.
Fig. 14 How to get the curved line distance between two points
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(f) Find the distance by measuring it along the linear scale as you did for the straight line distance.