BS: Map Projections

Subject: BS: Map Projections
From: robomatic
Date: 17 Mar 18 - 09:46 PM

I lived in an international house for a year of college; I was one of four U.S. Americans in a shared home of 26 people from around the world. No magic to it, it was primarily lived in by graduate students from a long ways away- too far to travel home to on short or medium vacations. I was in a similar situation within my own country. We also did not eat on the University dining system: We cooked and cleaned and ate on a cooperative basis, but were allowed to purchase basic food supplies throught the commisary. We could save a lot of money because we were our own cooks and servers. Some of us also learned to cook well and interestingly (Some of us, of course, not). This led to a very interesting working experiment, an 'experiment' without a control group. There were Hindus, Buddhists, Jews, Christians, Muslims, Western Bloc, Eastern Bloc, Indian, Pakistani, White South African, Black African, and weirdest of all, Californians in residence.
We had some interesting experiments within the experiment. Someone wanted to collect information on how many of the residents were virgins. Someone bought a huge world map from the American government (USGS) which came in three large sections with the United States at the center. We were all going to insert push pins to show our points of origin. This person mounted the map up with the sections out of intended order- they still showed the world, but with the United States off to the sides.
This was the high point of college life for me. When the TV show "The West Wing" came along a generation later, the episode wherein a different map projection than the one most Americans are used to rang a bell for me. It still has something to say today.

Subject: RE: BS: Map Projections
From: Senoufou
Date: 18 Mar 18 - 05:16 AM

Subject: RE: BS: Map Projections
From: Senoufou
Date: 18 Mar 18 - 05:25 AM

Good heavens, Mudcat posted before I'd written a single word! Is it haunted???
I find this all extremely fascinating robomatic. I watched your clip, and it's never occurred to me before as significant that most of the Third World countries are indeed 'on the bottom' of the Mercator map (apart from Australasia), which could give rise to ideas about 'superiority' of developed lands.

I've always known the the Mercator distorts the landmasses, but accepted that it was to make the whole thing more accessible.
Africa is indeed much larger than the Mercator would suggest. And one could turn the globe around and put any country at the centre of a map, since the Earth is a sphere. In Victorian times, wealthy families employed governesses who always used 'The Globes' with which to instruct their pupils. This would seem more accurate, but not very practical.
I'm also very interested in your multi-national student accommodation. I'd have been in heaven, as I'm an incurable xenophile.

Subject: RE: BS: Map Projections
From: DMcG
Date: 18 Mar 18 - 05:57 AM

As a map is a two dimensional representation of a three dimensional object, however you represent it must be a distortion. You pick the distortion to minimise errors in the aspect you care about. So the mercator projection was designed to preserve bearing from any point to any destination. That is more important for a sailing ship than preserving sizes of countries. Other projections keep area better but lose the bearing preservation.

You sometimes here people claim one projection is better than another. That's meanless, really. One projection can be better than anothor for a given purpose, not in any absolute sense.

A different, but related question is the point of origin and orientation. The mercator projection has its origin as the intersection of the Greenwich meridian and the equator, But you could pick any other point as the origin. In the middle ages Jerusalem was often picked for maps. There are old maps with China at the focus. I have seen - admittedly tongue in cheek - maps with Australia as the centre and 'south up'. This choice is important for pyschological reasons more than operarional use


Then again, tiles used in SatNavs do not use the same origin for the whole map.

This is surprisingly large subject and one I had some involvement in in the early 1980s.

Subject: RE: BS: Map Projections
From: Steve Shaw
Date: 18 Mar 18 - 06:16 AM

I had a large Peters world map on my classroom wall for years and used it to provoke discussion about how we see things. Like any 2D representation of the globe, it distorts shape, in this case the distortion getting ever greater the further from the 45-degree north and south parallels you moved. The most striking thing that hits you at first is that both Africa and the Americas are rendered "long and thin." The claimed advantage of the Peters map was that it showed countries in the correct area relationships with each other, ostensibly doing away with the potential for "cartographic imperialism." Of course, that depends also on who you put in the middle of the map :-) The controversy rumbles on!

Subject: RE: BS: Map Projections
From: Black belt caterpillar wrestler
Date: 18 Mar 18 - 07:19 AM

The earth is not an exact sphere which makes more problems for map makers when in pursuit of the best fit for their maps. There are a series of different slightly distorted spherical shapes (spheroids) that are used for different parts of the world. They have strange names like Airey 1881, Indernational 1924 and WGS 84.
I found out about them when I used to work at the Hydrographic Office. The problems come when you try to fit two maps edge to edge and they have been based on different spheroids!

Robin

Subject: RE: BS: Map Projections
From: Iains
Date: 18 Mar 18 - 07:28 AM

" The controversy rumbles on! "
Best not talk about the Piri Reis maps then. Do they show South America, or Anarctica(ice free)?

Subject: RE: BS: Map Projections
From: Iains
Date: 18 Mar 18 - 11:10 AM

WGS 84. The World Geodetic System or WSG assumes a coordinate origin at the center of the mass of the earth. The last revision was made in 1984 and is referred to as WSG84. It is the reference system being used by the global positioning system or GPS which has now assumed universal usage for helping people to find their way to their destinations or to pinpoint their locations. As per this the ellipsoidal height of Mount Everest is 8823.51, whereas the Geoidal height is 8846.10 meters. The latitude and longitude positions remain the same.

Subject: RE: BS: Map Projections
From: Steve Shaw
Date: 18 Mar 18 - 01:41 PM

Best not talk about Piri Reis? And why may I ask should I not talk about my favourite Indian vegetarian dish??

Subject: RE: BS: Map Projections
From: robomatic
Date: 18 Mar 18 - 03:39 PM

Senoufou:

There were many heavens involved. Since it was a co-ed environment of young people in a liberated era and area, there were innumerable pair-ups, particularly of young people from parts of the world that had taught them the 'other' was the 'enemy'.
My pairing was antipodean.

Wonder if the shape of the world has something to do with the English phrase of things going 'pear shaped'?

Subject: RE: BS: Map Projections
From: Senoufou
Date: 18 Mar 18 - 03:55 PM

It sounds lovely robomatic. I had two very good friends at Uni, a Chinese lass and an Indian lady. My husband and I seem to collect different nationalities. At present (in addition to everyone in our village and old friends from way back) we know a Kenyan, a Gambian, an Angolan, a Zimbabwean, a Nigerian, a Burkinabe couple, a Ghanaian and, a Bangladeshi couple. And most of Adjame in Abidjan!

I've always loved maps, and enjoyed teaching my pupils over the years to cope with six-figure OS Map references and understand all the OS symbols.

Subject: RE: BS: Map Projections
From: JennieG
Date: 18 Mar 18 - 11:02 PM

But....but.....but.....you mean to say it isn't flat after all?

Saw a funny on facebook a while ago which said "The only thing flat earthers have to fear is sphere itself". I thought that was hilarious.

Subject: RE: BS: Map Projections
From: Senoufou
Date: 19 Mar 18 - 03:03 AM

That's priceless Jennie!

Subject: RE: BS: Map Projections
From: Steve Shaw
Date: 19 Mar 18 - 05:15 AM

And flat-earthism has become a global phenomenon...

Subject: RE: BS: Map Projections
From: Iains
Date: 19 Mar 18 - 05:51 AM

And the world is becoming terror formed.

Subject: RE: BS: Map Projections
From: Jos
Date: 19 Mar 18 - 07:14 AM

At least if you are a flat-earther with a round map it is fairly easy to avoid falling off the edge. That map with spikes and gullies could be quite dangerous.

Subject: RE: BS: Map Projections
From: Steve Shaw
Date: 19 Mar 18 - 08:37 AM

That's just a typical flat-earther circular argument.

Subject: RE: BS: Map Projections
From: DMcG
Date: 19 Mar 18 - 09:05 AM

Flat earthers? Pah! I am a Riemann Manifoldian myself.

Subject: RE: BS: Map Projections
From: Senoufou
Date: 19 Mar 18 - 09:29 AM

Anyone born and bred in Norfolk could be forgiven for thinking the Earth is flat. Very flat...

Subject: RE: BS: Map Projections
From: DMcG
Date: 19 Mar 18 - 09:33 AM

Subject: RE: BS: Map Projections
From: Rob Naylor
Date: 19 Mar 18 - 09:56 AM

IainS:WGS 84. The World Geodetic System or WSG assumes a coordinate origin at the center of the mass of the earth. The last revision was made in 1984 and is referred to as WSG84. It is the reference system being used by the global positioning system or GPS which has now assumed universal usage for helping people to find their way to their destinations or to pinpoint their locations. As per this the ellipsoidal height of Mount Everest is 8823.51, whereas the Geoidal height is 8846.10 meters. The latitude and longitude positions remain the same.


Actually, WGS84 is a dynamic system itself, and under constant revision. WGS84 coordinates of a spot you measure today are likely to differ from WGS84 coordinates measured for the same spot a number of years ago. Revision is partly due to continental drift, and partly due to improvements that are constantly being made to the gravitational model of the earth.

Below is an extract of the Abstract of a paper I will shortly be giving to the Society of Exploration Geophysicists:

"ITRF (International Terrestrial Reference Frame) is the fundamental reference datum used in Geodesy and is realised by large networks of fiducial sites comprising GPS; Satellite Laser Ranging (SLR); Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) station coordinates which are defined at a Reference Epoch and with associated site velocities (to account for tectonic movement). This means that ITRF is a dynamic reference system whose coordinates are changing over time to reflect tectonic movement on a global scale.

It is less well-known that the WGS 84 CRS is also dynamic in nature, as the ground stations used to define the system are part of the ITRF definition system. The datum is defined by the coordinates and velocities of 18 GPS tracking stations. Each realisation of the WGS 84 datum is designated by the GPS week number of its inception. WGS 84 is kept in alignment with ITRF at the sub-decimetre level to ensure that the GPS Broadcast Ephemeris is not degraded by holding coordinates of the GPS tracking stations fixed when in fact they are moving tectonically.

This means that the WGS 84 coordinates of a point measured using GPS in, say, 1998, are likely to differ from WGS 84 coordinates of the same point measured in, say, 2018."


This whole topic is quite complex. The huge number of significantly large errors we see in maps, databases and data management systems are largely as a result of people without a requisite detailed knowledge of Geodesy and Cartography using inappropriately the easily-available systems for both data acquisition (eg GNSS such as GPS or GLONASS) and data manipulation (eg GIS systems such as ArcGIS).

Subject: RE: BS: Map Projections
From: Iains
Date: 19 Mar 18 - 10:36 AM

Rob Naylor Thanks for that correction and elaboration. I have only used it indirectly for UTM coordinates based on the WGS84 ellipsoid, when having borehole locations surveyed. As you say it is a complex subject, and I have vast gaps in my knowledge.

Subject: RE: BS: Map Projections
From: Rob Naylor
Date: 19 Mar 18 - 11:38 AM

I still have gaps in mine, and I've been studying it for over 40 years! I first did field work with GPS in 1985, when we had 25 minutes coverage a day in most parts of the world.

One country I'm advising at the moment has decided to standardise its CRS in WGS84 based on the ITRF2000 realisation. So its CRS is WGS84(ITRF2000.2000). Data being logged now is in WGS84 based on ITRF2014 at the current epoch (WGS84(ITRF2014@currentepoch)). I'm finding differences of well over a metre at some sites when I transform the data back to WGS84(ITRF2000.2000).

As requirements for precision in seismic surveying, well and borehole drilling and renewables installations have become tighter and tighter, these time-dependent coordinate changes, which we ignored until recently, are starting to show up as issues to be addressed. Which kind of negates the comments I still get from OIMs and the like saying, essentially, " we don't need surveyors any more, we have GPS.....anyone can be a surveyor now...." :-)

Subject: RE: BS: Map Projections
From: robomatic
Date: 19 Mar 18 - 07:40 PM

Holy Crap Rob Naylor I didn't expect an exegesis on terrestrial frames of reference (if, indeed, that was what it was). A school mate of mine from elementary days had an obsession with Mt. Everest. I used to make him schoolkid drawings and pass them in class about how Mt. Everest could be improved in the service of man: internal elevators, parking lots on top, Tastee Freeze or elaborate bird sanctuary where all their crap wouldn't freeze, re-name it to something more American, preferably in honor of The Red Sox. This same kid told me that one of the detailed surveys made in precisely estimating the up-top altitude came out to 29,000 feet exactly but this looked like it lacked enough significant figures so they added a few feet to make it look righteous!

JennieG I laughed aloud at "sphere itself!" I hope that went into my permanent memory.

Subject: RE: BS: Map Projections
From: robomatic
Date: 19 Mar 18 - 07:45 PM

"bird sanctuary where all their crap would stay frozen was what I meant, but my word bubble suffered a collapse and I had to re-write a lot of it and I didn't proof read very well, as is my wont.

If I understood Rob Naylor's long post, above, it was that in fixing locations in the most sophisticated manner now possible we are not using 'sea-level' we are using the actual center of the earth as three dimensional (Cartesian) origin (0,0,0) so that various precise digital devices can coordinate.

Did I get that right?

I won't worry about it until I find someone is re-configuring everything to relate to the Center of the Sun.

Subject: RE: BS: Map Projections
From: Steve Shaw
Date: 19 Mar 18 - 10:00 PM

The earth hasn't really got an exact centre because it's constantly being pulled around by the sun and moon, etc., not to speak of all the wobbly stuff going on in its runny bits inside, and is changing shape a bit all the time. All those oceans keep moving around too and you can't not count them. Anyway, I'm still happy with the height given for Everest by Arthur Mee's Children's Encyclopaedia, the ten volumes of which I devoured as a child and which made me what I am. That height was 29002 feet. That extra "two" on the end made it so easy to remember. I always remember that Penyghent is exactly one hundred feet lower than Ingleborough and that Liathach is 3456 feet. I wasn't bad at rods, poles, perches and chains either. I'm quite good at converting fat into stones too, unfortunately.

Subject: RE: BS: Map Projections
From: Rob Naylor
Date: 20 Mar 18 - 09:00 AM

robomatic: Holy Crap Rob Naylor I didn't expect an exegesis on terrestrial frames of reference

Ha!......NOBODY expects an exegesis in terrestrial frames of reference...................Cardinal Fang.....the COMFY CHAIR!

Subject: RE: BS: Map Projections
From: robomatic
Date: 20 Mar 18 - 12:37 PM

LOL

Some of the representatiional art of the Northwest Coastal tribes of British Columbia seems to be a 2-D interpretation of 3-D: To put it simply the art is a conceptual skinning of the animals. Totem Poles are a kind of re-mapping of the animal face and skin onto a cylinder. They can be quite evocative. The tribes cross boundries so they exist in Alaska, usually called Southeast Coastal from our frame of reference.
When in Vancouver BC I visit the Museum of Anthropology at University of British Columbia, which I used to call the "Totem Pole Museum" and here is a youtubetour of the Bill Reid Gallery at Simon Fraser University

Subject: RE: BS: Map Projections
From: Iains
Date: 20 Mar 18 - 07:21 PM

"NOBODY expects an exegesis in terrestrial frames of reference."
It is kind of handy to be aware that no matter how many decimal places are used to define x,y,z there is still uncertainty. This is especially true when it comes to plotting a well azimuth and inclination. For downhole surveys there are apparently nearly 100 sources of potential error and when horizontal sections can be up to 15000m in length the ellipsoid of uncertainty at the end of the wellbore can be quite large. Even the measurement of length is subject to error. I have never seen the total depth defined by wireline and drillpipe agree in vertical holes and that is over a span of 45 years.

Rather than Monty Python I prefer what have the Romans done for us.

https://www.youtube.com/watch?v=3qTRRBEkesA

Subject: RE: BS: Map Projections
From: JennieG
Date: 21 Mar 18 - 01:50 AM

Eliza and Rob, you're welcome!

Subject: RE: BS: Map Projections
From: radriano
Date: 21 Mar 18 - 05:13 PM

Map Projections from the US Geological Survey

Can be downloaded free of charge here:

https://egsc.usgs.gov/isb//pubs/MapProjections/projections.html

https://www.scribd.com/doc/92268542/Map-Projections-Poster-USGS

Subject: RE: BS: Map Projections
From: Nigel Parsons
Date: 21 Mar 18 - 06:05 PM

Map projection is fine, as long as you have a spherical (or oblate spheroidical) wall to project onto ;)

Subject: RE: BS: Map Projections
From: robomatic
Date: 23 Mar 18 - 09:33 AM

When I was a kid in MA our public school teachers took us on more than one visit to the Christian Science mother church in Boston. I'm not sure of the justification for it, our good mostly Catholic and Protestant teachers weren't trying to convert us to the religion founded by Mary Baker Eddy. -Maybe we were subjects of a form of Massachusetts pride- They were fun trips and the highlight was a walk through the mapparium. The mapping in this case was a kind of direct scaled down negative (inverted?) mapping. It was a kind of 'freaking me out' experience, and a welcome one, because it was totally understandable, but different.

My mother subscribed to the Christian Science Monitor for many years. It seemed to hold an unprejudiced interest in the world and always had some kind of in-depth international article in its pages which was printed twice, once in English, and again in some other language.

According to this article, there are interesting acoustical effects in the Mapparium, which I'm sure we enjoyed when we were walking through, but I don't explicitly remember them.