All Maps in China are Transformed • Hacker News Board

Re: All Maps in China are Transformed

#111

Post by pekk » Mon, Oct 31, 2011, 3:41 PM UTC

rmc wrote: post #66

nate_meurer wrote: post #57

Earlier quoted context omitted.

Mercator distortion has nothing to do with the anecdote in the parent post. There the allegation was of deliberate inaccuracy, which renders a map non-functional for most purposes. All 2D map projections produce either distortion or discontinuity. Neither of these affects a map's functionality in the way that outright inaccuracy does.

Oh yes, I agree that this is an example of purely the geometry, not a political attempt. But I know people who , upon seeing the distortion, were surprised at how many maps were "wrong". This shows that you can't rely on the market to weed out inaccurate maps. After all, a map that had the south at the top (rather than the bottom) would be viewed as "wrong" and would be penalized with poor sales. The idea that the ma…

"you can't rely on the market to weed out inaccurate maps" is a misleading statement, particularly in the context where people are contending that the size of Taiwan has intentionally been inflated worldwide for political reasons.

THAT kind of inaccuracy bears almost no resemblance to gripes which emerge about the tradeoffs in 2d map projections regarding inevitable (as opposed to highly arbitrary, political) shape and area distortions.

Maps which have south at the top ARE sold and do just fine in the Southern Hemisphere.

The point actually remains that the market has not rewarded any maps which have the kind of distortions which would be required to specifically and artificially inflate the size of Taiwan relative to China, without much affecting anything else.

Re: All Maps in China are Transformed

#112

Post by pekk » Mon, Oct 31, 2011, 3:43 PM UTC

bigwally wrote: post #15

This is not a problem with using a GPS, the problem is the shift from using different mapping technologies. Trying to get satellite and the map portions to line up is very difficult. Trying to do it on a global scale with data from multiple sources... you get the idea. Now please get back to China bashing and don't let the facts get in the way of your political/religious feelings. Remember to include lots anecdotal e…

While I agree - in different words - that it's probably just a projection error, it is always extremely off-putting when the Overbearing Defensive Cyber-Army makes its appearance to defend China from any and every possible criticism.

It really does much more harm to China than a simple misunderstanding about projection errors.

Re: All Maps in China are Transformed

#113

Post by alexqgb » Mon, Oct 31, 2011, 3:45 PM UTC

Sniffnoy wrote: post #72

alexqgb wrote: post #62

Earlier quoted context omitted.

The Mercator projection isn't a good example of a map in which visual distortion and a lack of navigational utility go hand in hand. Indeed, the hole point of the projection was to make navigation easier by allowing rhumb lines (the shortest distances between two points on a curved surface) to be charted as perfectly straight lines on a two-dimensional map. From these lines of constant bearing, mariners could work ou…

Let's not get mixed up about what the projection did and didn't do. As you point out, the importance of rhumb lines comes not from the fact that the thing they keep constant -- the bearing (with respect to north/south) -- was something that could actually be measured. Rhumb lines are not, however, the shortest distance between two points on a sphere. Those would be great circles. In particular, note that along a rhum…

Indeed, Sniffnoy - thanks for sorting out my terminology. Great circles is exactly what I meant.

Re: All Maps in China are Transformed

#114

Post by alexqgb » Mon, Oct 31, 2011, 3:49 PM UTC

pekk wrote: post #110

Sniffnoy wrote: post #79

Earlier quoted context omitted.

Argh. Misnegation from earlier version. "As you point out, the importance of rhumb lines comes from the fact that..." -- there shouldnt' be a not there.

You are (it seems intentionally) ignoring the point that Mercator's area distortion doesn't dangerously mislead in navigation, quite the contrary. Or, if that isn't true, please name some cases where navigators were messed up because they thought Greenland looked bigger than it was in area. Unless you use a globe, every projection onto a flat rectangular surface distorts. Now how does that make more plausible the cla…

Really? Seemed like he was simply pointing out an error on my part. Don't see where Taiwan enters that at all.

More to the point, there's a big difference between distorting scale in a way that's mathematically consistent throughout the projection (i.e. one in which you preserve shape or position at scale's expense), and simply fudging the scale in a particular spot.

Re: All Maps in China are Transformed

#115

Post by waqf » Mon, Oct 31, 2011, 8:03 PM UTC

rmc wrote: post #105

nate_meurer wrote: post #92

Earlier quoted context omitted.

I see what you're saying. I agree. As an aside, I have often wondered at the way North=up became, and remains, completely universal. An upside-down globe "looks" as wrong to me as an upside-down portrait. Obviously there's no reason this must be so; it's nothing more than familiarity with the shapes of the continents from a particular perspective. Some day, I'd like to have a globe or a big mercator-type map with Sou…

In early times, east was up and north to the right. Apparently an Australian group made a south is up map

Isn't that backwards? If east were up, north would be to the left. Unless you're making a celestial map.

Re: All Maps in China are Transformed

#116

Post by rmc » Mon, Oct 31, 2011, 9:47 PM UTC

waqf wrote: post #115

rmc wrote: post #105

Earlier quoted context omitted.

In early times, east was up and north to the right. Apparently an Australian group made a south is up map

Isn't that backwards? If east were up, north would be to the left. Unless you're making a celestial map.

Yes, you're right, my mistake. I was thinking of an old map I saw that had west up and north right.

Re: All Maps in China are Transformed

#117

Post by kleim » Tue, Nov 01, 2011, 12:35 AM UTC

This is so ridiculous. China really thinks US Army is using Google maps? I wonder how they did not figured out that all armies are not working like theirs...

Re: All Maps in China are Transformed

#118

Post by mapster » Wed, Nov 02, 2011, 3:20 PM UTC

srl wrote: post #36

mapster wrote: post #34

It could simply be a map projection issue - where the traffic data projection is slightly off by an order of 1000 meters. This datum shift could be easily fixed by Google.

A map projection issue would show up in other places on the map, and would have been fixed by now.

Not true at all. Data can be pulled from multiple database sources, each with their own projection info., so if there are datum shifting issues, you can have some pieces not aligning to basemap while others do.

Re: All Maps in China are Transformed

#119

Post by Sniffnoy » Wed, Nov 02, 2011, 11:11 PM UTC

alexqgb wrote: post #113

Sniffnoy wrote: post #72

Earlier quoted context omitted.

Let's not get mixed up about what the projection did and didn't do. As you point out, the importance of rhumb lines comes not from the fact that the thing they keep constant -- the bearing (with respect to north/south) -- was something that could actually be measured. Rhumb lines are not, however, the shortest distance between two points on a sphere. Those would be great circles. In particular, note that along a rhum…

Indeed, Sniffnoy - thanks for sorting out my terminology. Great circles is exactly what I meant.

Really? I think you meant rhumb lines. :) They're both important, just for different reasons; and it's rhumb lines that are easily visible on a Mercator projection and that were so useful for navigation.