Friday, August 29, 2014

Explaining Map Projections with GMEL (Google Maps Engine Lite)

This is the second post in which I write up ideas I've lifted from colleagues at the Google Teacher's Institute I went to in Pittsburg earlier this year.  This time I'll work up an idea I got from Josh Williams, author of  Use the polygon (shape) function in google maps engine lite to illustrate distortions produced by projections.

Background to Projections:  A problem with all flat maps is the 'orange peel problem' - try as you might there is no way to peel an orange and get the peel to lay flat without stretching it (if it was made of rubber) or ripping it into very small pieces.  All flat map representations of our globe are therefore distorted in some way.

0] You may like to start with some demo of actually peeling an orange and trying to get the peel flat.

1] Using Google Earth show students Greenland and South America to illustrate the size difference.  You might like to use the ruler tool to actually measure the width/height.  South America is much the larger.

2] Now flip to Google Maps Engine Lite and create a new map by clicking the button (you'll need to login to Google if you aren't already)

3] Name the map 'Illustrating Projections' or something similar

4] Point out to the students the difference in apparent size now, why would Greenland appear to be the same size as the much bigger South America?  The answer is distortion.

5] Using the 'draw a line tool' (a line separated by circles in a button under the search bar) click and release four times to create a big square covering Brazil.  It will have circles at the corners to show it is the item you are editing at the moment.

6] Tell the students you're now going to drag it northwards over Greenland and that the surface area it encloses is going to stay constant.  Get them to predict what is going to happen to the square in a sketch on paper.

7]  Now click the square so it has circles (being edited) and drag it northwards.  The distortion shows up in three ways:
a] it gets bigger
b] it gets wider at the top at the bottom as the distortion increases closer to the poles
c] edges become curves, again, due to the distortion increasing as you go north.

8] Process with students, e.g. I'd ask if anyone got all three.

1 comment:

Josh Livni said...

This a nice interactive way of showing projections via a geography guessing game: