## Wednesday, December 14, 2011

### Drawing Simple Scale Map by Triangle Method

To draw a map with the method described herein, you do not need to go to the objects to be mapped to measure object distances one by one. But those objects should be visible from a distance. Only one measure of the distance that needs to be known as the reference, other distances will be known later. The tools used are:

• pencil, preferably cylindrical as easy to roll
• ruler
• paper
• distance measuring tool, if necessary

The method is similar to the method in the article Distance Measure by Paper, Ruler and Pencil, which describe how to measure the distance by triangle method with only single landscape object to make it simple and easy to understand.

In the following example, will be drawn a map of an area with some object that are: a house, a tower with a tank of water, road, tree, as shown below:

There is a road with distance mark, and it is known that distance from point A to point B is 200 meters. On the left side of the road, or at the top of image, there is a house near point A, and a tower with a water tank at near point B. On the left side of the road, or at the bottom of the picture, there is a tree. It is needed to have a map with scale that is accurate enough to describe the situation of that landscape.

How to draw a scale map:

Prepare a flat and level area, can be a table or board. Table can be leveled by putting pencil with cylindrical body on that table, pencil should not be roll in the direction of table length, and that pencil is also not rolling along the direction of table width. This table will be used as a base for drawing the map. This table should be moved to point A and to point B, unless there are two tables, one at point A and one at point B.

At position A

Make sure the table in a flat position. Put a piece of blank paper on the table. Draw the a-b line that representing the path from point A to point B. Position the a-b line on the paper so there is enough space for drawing other objects.

Ratio of the length of a-b line on the paper with path length from point A to point B will be the scale of this map. Suppose a-b line length is 20 cm, with distance of point A to B is 200 meters, then the scale of the map is:

Scale = 20 cm: 200 meters = 20: 20,000 = 1: 1,000

Position the paper so that the a-b line is in line with an imaginary line from point A to point B on the road. Make sure the paper does not move when a-b is in line with AB.

Place the ruler at point ‘a’ on the image, then aim the ruller towards the house on the landscape, draw this imaginary line on the paper. This line will determine the house position on the map.

By aiming the ruler from point ‘a’ to the water tank, then the imaginary line from A to the water tank can be drawn. Do the same for the imaginary line from point A to the tree.

At position B

Now move to position B. Make sure the table at level position. Position the drawing paper so that the line a-b on the picture is in line with an imaginary line from point B to point A. Make sure the paper does not move in this position.

Aim ruler from point b to the house, then draw the line on the map. Then the intersection of the lines will show the house location on the map, shown in the figure below as a red dot.

Aim ruler from point b to the tank water, then draw the line on the map. Then the intersection of the lines will show the location of water tank on the map, in the image below it looks as blue dot. Do the same thing on the tree, seen in the figure below as green dot.

Now it can be seen on the map each objects position to represent the position of objects of the landscape. You can erase all temporary lines, and drawing objects on the map.

To calculate the distance of each object, we can use the scale of the map that was calculated previously, for example:

The distance from a home on the map is 20 cm, the distance on the landscape are:
20 cm x 1,000 = 20,000 cm = 200 meters

The distance from b to a water tank on the map is 25 cm, the distance on the landscape are:
25 cm x 1,000 = 25,000 cm = 250 meters

The distance from a to a tree on the map is 15 cm, the distance on the landscape are:
15 cm x 1,000 = 15,000 cm = 150 meters.

This triangle method to draw a map is quite accurate, although it’s tools are very simple and very easy procedure. The resulting map can be used for measuring distances, calculate the area of ​​land, landscape planning, etc.. Of course it will be much more accurate if using Theodolite or Total Station, an instrument which is used by surveyor, geodesy expert, cartographer, etc..

You can play treasure hunt game with a map drawn by this triangle method.