Map Making- Hypothetical Example
Click here to go to the map making topic's first page. (You should read that page before attempting the following.)
A hypothetical group of children when out into a hypothetical field, and noted the following, in order to make a map of the field.
From above, i.e. as it would appear on a map, the field was 'L' shaped.
Starting in the north-west corner, the children 'named' the corners of the field, counter-clockwise, (i.e. 'anti-clockwise... same thing) A, B, C, D, E and F.
They measured the following angles:
ABC 90 degrees
BAC 34 degrees
BAD 46 degrees
ABD 66.5 degrees
BAF 90 degrees
ABF 18.5 degrees
ABE 46.5 degrees
BAE 26 degrees
With that information, and the ideas set out on the first page of this, you can draw a map of the field! It may help you to know that a piece of A4 or 8-1/2" x 11" paper will do fine. Turn it portrait- wise. (Not landscape. In other words, have the short edge nearest you.), Put 'A' about 3cm from the top left corner. Put 'B' 18cm below 'A'. (These points can be anywhere on the page... but if you put them in the 'wrong' places, you'll need a bigger piece of paper if you are going to get everything in.)
Once you have drawn all the lines implied by the angles above, you should get an 'L' shaped field. Don't worry if it isn't 'exactly' right.... just do what the numbers tell you you must!
Now... if it were a perfect world, you would have a perfect map. But the world isn't perfect. Therefore, scientists and engineers look for ways to check their work, ways to spot errors, ways to make results more nearly perfect.
The children went back to the field. The went to a place half way between A and B. Because it was half way between A and B, it was easy to mark it's correct position on the map they were making. They called this place G. They then collected the following measurements:
AGC 126.5 degrees
AGD 106 degrees
AGF 34 degrees
AGE 126.5 degrees
Draw those angles in on your map. IF.....
BAF is really exactly 90 degrees, AND
ABF is really exactly 18.5 degrees, AND
AGF is really exactly 34 degrees, AND
You draw all three angles just right, the lines going towards F will all cross in the same place.
By measuring more angles than he/she 'must', the map maker creates information which will check the information he is using to draw the map.
Now.... have you really done what you should, according to the instructions above? There are two 'tricks' in this page's information which will help you or your teacher see. When you are sure, sure, sure that you have done everthing properly, click here to see what the 'tricks' were.
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