[OSM-dev] Plotting data on an equirectangular map, distorted for sphere projection

Christopher Stevens chris at christopherstevens.cc
Thu Jul 18 02:35:50 UTC 2013

Hello Dane,
Thanks for taking a look. So far I can produce an EPSG:4326 image nicely,
your comment boosted that setup (thanks!). This one is quick and ugly, but
should work for illustration purposes:

Now to add some basic large labels:

If I then project this on a sphere (virtual one in this example, but looks
the same in real projection), the geography placement looks great and lines
up well with other datasets. The styling gets odd with labels and lines
getting thinner horizontally.
http://www.flickr.com/photos/8139783@N08/9309514621/in/photostream/ - side
http://www.flickr.com/photos/8139783@N08/9309514685/in/photostream/ - pole
view, the presenter often turns the globe this way for audience

Let me know if that helps illustrate the challenge better.

Thanks again,


On Wed, Jul 17, 2013 at 11:41 AM, Dane Springmeyer <dane at dbsgeo.com> wrote:

> Chris,
> It would be helpful to explain what you've tried already. Mapnik supports
> proj4 and proj4 understands quite a few projections. I'm no expert in
> equirectangular projections but
> https://en.wikipedia.org/wiki/Equirectangular_projection states that this
> is basically a term for the well know set of lon/lat based geographic
> coordinate systems.
> So, can you try simply changing your Mapnik Map `srs` value to EPSG:4326
> or a specific Equidistant cylindrical projection like
> http://spatialreference.org/ref/epsg/3786/
> The specific Mapnik Map XML syntax can be found by following the link for
> "Mapnik XML" like:
> http://spatialreference.org/ref/epsg/3786/mapnik/
> Dane
> On Jul 17, 2013, at 9:41 AM, Christopher Stevens <
> chris at christopherstevens.cc> wrote:
> Hello gurus,
> I'm thinking that I may need to find some alternative data visualization
> software to make this work, but I love mapnik and thought it would be good
> to start here first.
> I'm hoping to create a basic themed map of different types of data and
> plot it on a full-Earth image (I can figure this part out, starter examples
> cover this as well). The challenge is that I'm then projecting this on Science
> On a Sphere<http://www.spacefoundation.org/visit/northrop-grumman-science-center-featuring-science-sphere/science-sphere%C2%AE>,
> which requires equirectangular images that distort more towards the poles.
> Here's a quick example of something I made in a 3D program to show latitude
> and longitude lines (note how the lines and labels get fuzzy and stretched
> near the poles).
> http://www.flickr.com/photos/8139783@N08/9305646391/
> Is there a way to add this type of distortion in mapnik? I'm guessing not
> as mapnik is optimized for other uses (but who knows). I'm guessing that it
> would "work" as is, but labels would get distorted (there are
> work-arounds), and lines would get very thin near the poles.
> Thanks for the feedback in advance. Let me know if I can answer any
> questions.
> Best regards,
> Chris
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Christopher Stevens
303.929.7863 cell
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