Size comparison maps are very popular, and can be found all over social media. Are there any geographic mathematical principles which completely dispel them. Can we comfortably assert they are neither accurate nor precise or should I admit they have some legitimacy? Here is an example below "Size comparison of the Great Barrier Reef and Central Europe." Is it fair to say that any map (no matter what projection) is inherently distorting area. Such a comparison is deceptive to the eye, while appealing like candy? Making these maps is utter nonsense. A simple numerical calculation would have more significance.
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leaflifelayf
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1A map that uses web mercator is wrong from the start... does that count? – DPSSpatial_BoycottingGISSE Oct 08 '15 at 21:51
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Yeah, these size comparisons are wrong if web maps are being used (such as google maps) as they are in web mercator projection which does not preserve area. If you see a google map area comparison, generally, it's going to be wrong. – Thomas Oct 08 '15 at 21:52
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Yes, plenty of jibs at google, but putting that aside. Do these maps break all the logical principles of cartography? Are they intended to stupefy, serving no purpose at all? – leaflifelayf Oct 08 '15 at 22:21
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1@leaflifelayf isn't that a very subjective question? and we're not jibing google, we're pointing out that whether or not they are 'logical', they are straight up WRONG if they're plotted in web mercator. – DPSSpatial_BoycottingGISSE Oct 08 '15 at 22:28
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1I think size comparison maps are wrong in general. They are deceptive no matter what projection they are in. – leaflifelayf Oct 08 '15 at 23:06
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1There's a number of questions in this question, many of which are primarily opinion-based. – Vince Oct 08 '15 at 23:52
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@Vince oh really? – DPSSpatial_BoycottingGISSE Oct 09 '15 at 00:48
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"Making these maps is utter nonsense." sounds like an opinion. – PolyGeo Oct 09 '15 at 01:47
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@PolyGeo maybe it's a rhetorical statement used to generate thought on the subject... – DPSSpatial_BoycottingGISSE Oct 09 '15 at 12:46
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It depends on the map projection.
If both the source of country polygon, and the overlay/basemap are using equal area projections (which are not common, especially on webmaps) then yes a size comparison is 100% fair. Otherwise, no, different amounts of areal distortion are found at different parts of the globe.
Further reading: http://www.progonos.com/furuti/MapProj/Dither/CartProp/AreaPres/areaPres.html
Thomas
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I understand your point, but these maps are totally chauvinist. I enjoyed the links. Why do you think a size comparison is so important to people? – leaflifelayf Oct 08 '15 at 22:29
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One particular example which takes into consideration size as well as cultural and social relevance is this map of Detroit which has made the rounds for several years:
In this example, we cast our doubts about projections aside, and can focus on the meaning.
In the case of Detroit - just how big is it?
We all know how big the cities of Boston, New York, and San Francisco are, and we all hear about how cruddy Detroit has gotten - but the context of this is just how much vacant land Detroit has, and what that means in relation to other major Cities.
So I would think given a relevant problem such as this, that 'comparison maps' DO have meaning and DO use proper geographic principles.
I have, for example, recreated this map using proper coordinate systems, etc. and found that it is valid... and for someone like me who has great interest in the City of Detroit, communicated a message of just how HUGE Detroit really is!!!
DPSSpatial_BoycottingGISSE
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@leaflifelayf much appreciate it - we must stick together in these times of deception!!! – DPSSpatial_BoycottingGISSE Oct 09 '15 at 19:00
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Yes, I found an answer. As you aggregate a map, the size is distorted, especially when viewed over the web. Projections are based on different surfaces and distort maps in different ways. Two images layered on top of each other will generally always distort the different areas on a map, making a size comparison completely useless. Here is an image I found, which is a humorous rendition to my point. Any more clarification would be appreciated. Here is an example which proves my point quite well.
leaflifelayf
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There are several problems with your arguments. Chiefly among them is the fact that not all map projections distort area. – alphabetasoup Oct 09 '15 at 01:27
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