
Look, Ma, No More Mercator Tiles - callum85
http://vis4.net/blog/posts/no-more-mercator-tiles/
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jameshart
Wouldn't the ideal approach be to have projections change as you scroll and
zoom around a map? Zooming into the corner of a conical map means that
directions get all skewed. At high enough zoom levels, you _want_ the
directional fidelity of mercator (or maybe a polar projection from the current
focus point).

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ryandvm
Right. I believe this what the National Weather Service does for their radar
maps. They're using a polar projection from the location of each station.
Points 100 miles north, south, east or west will all fall in a perfect circle
around the center of the map.

[http://radar.weather.gov/ridge/radar.php?rid=lgx&product=N0R...](http://radar.weather.gov/ridge/radar.php?rid=lgx&product=N0R&overlay=11101111&loop=no)

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Animats
There's much to be said for that. We used that for automatic driving, using
the starting point of the trip as the pole. This works well for trips of
moderate length. GPS coordinates in Earth-centered, earth-fixed form (a vector
from the center of the earth, which what you really get out of GPS) map easily
to this form.

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rlease
How does the projection change with all 50 states displayed instead of just
the contiguous ones?

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necubi
There's a special projection just for that:
[http://bl.ocks.org/mbostock/4090848](http://bl.ocks.org/mbostock/4090848).

"The Albers USA projection is a composite projection of four Albers
projections designed to display the forty-eight lower United States alongside
Alaska and Hawaii. Although intended for choropleths, it scales the area of
Alaska by a factor of 0.35x (a lie factor of 3); Hawaii is shown at the same
scale as the lower forty-eight."

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moron4hire
The trouble has always been the map data, not the drawing of the tiles. Anyone
with a highschool trigonometry education should be able to figure out the
drawing given the data.

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drivingmenuts
Seems like the point should be the data, not the shape of the map. How does
changing the projection type alter the information provided in this case?

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sgnelson
Yes, you're correct, the point should be the data. However, the projection
(not the shape), matters a great deal for a number of reasons. The classic
example is to take an orange peel and flatten it. It's impossible to do
without tearing or distorting in one way or another. The Earth is of course a
3d shape, and maps are 2d, thus projections to try and map the world as
accurately as possible. However, it gets more complicated when you project the
data, going back to the distortion. It becomes a problem of "Pick 2 out of 3."
That usually means Area, Shape and Direction. You can have an accurate
representation of Area and Shape, but not Direction. Or in the case of
Mercator, Direction and Shape, but not size. Mercator was used by ocean going
navigators so that they could draw a straight line on their navigation charts
(as longitude and lattitude lines are represented by rectangles with 90 degree
angles). Since then of course, we now have thousands of different projections,
used for different purposes so that we can try and create the most accurate
mapping of the "real" world as we can. And of course, the projection you
choose, should hopefully help you in accurately communicating that geographic
information to others. I hope that all makes sense.

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rburhum
Since my co-worker and I have been maintaining Tilestache, I am glad you
included it in your tutorial :)

