Even if you look at maps every day, you probably don’t think much about the process of how the globe (a 3D surface) is transformed into a map (a 2D surface).
In the age of web mapping, specifically Google Maps, many of the maps we view are in a projection called Web Mercator. This projection is similar to and based on the Mercator projection, which is fairly famous for distorting area of the high latitudes (e.g. Greenland isn’t as big as we all often think it is. Thanks, Mercator!).
Web Mercator is ubiquitous in mapping these days, which is great for some reasons, but pretty terrible in other instances. For instance, when we make a choropleth map (e.g. a map where we color each of the countries based on a value, say literacy rates) we give more visual weight to countries that are in the extreme north, because they look bigger (even if they aren’t!) just because of the projection.
We want you to scour the Internet for two maps, one that uses Web Mercator and one that doesn’t. Then you will compare and contrast the two maps in terms of their projections (not what they show on the map).
You have to have an eye for what Web Mercator looks like and be able to notice when something is not using that projection.
Here’s where to start:
1. Have a look at the following projection tools:
2. Get used to comparing how the different projections look different from Mercator or Web Mercator (for our little project here, just assume these are the same. They aren’t quite the same, but for right now, it doesn’t matter). I find that switching back and forth between different projections and Mercator is a great way to start seeing the differences.
3. Now find two thematic maps (see Chapter 3.2 in your e-textbook if you don’t remember what these are):
a. The maps can either both be of the contiguous United States (i.e. the lower 48) or both of the whole world. Make sure the geographic area matches between maps.
b. One map should be in Web Mercator and the other can be any other projection.
c. Paste a screenshot of both maps into the template. (use the Snipping Tool in Windows or Cmd+Shift+4 in Mac OS to save a screenshot to your desktop and paste into your template).
4. Compare and contrast the two maps by answering the following questions in well written college-level English. This should be in a paragraph form with a topic sentence.
a. Can you identify your non-Mercator map projection? Try using the tools to see if you can. Don’t worry too much if you can’t.
b. What is the difference between the two projections? Think in terms of what you know about projections from what you have read.
c. Is this map projection better for a thematic map than the Mercator map? Remember: Mercator is known to distort areas which is not ideal for illustrating mapped area data (e.g. a choropleth type of map). Does your other projection do a better job? Why?
d. Can you tell what aspect of the globe your projection distorts (i.e. size, shape, distance, or direction)?
e. Is it a compromise projection? How can you tell?