that is probably a very obvious question but it is melting my brain:

when transforming lat and lon to [x,y] (for instance using this code https://gist.github.com/RandomEtc/476238) I get the following: { x: -0.27, y: -1.12 }

What are x and y? Are these radians? How can I use x and y to find the exact point for that lat and lon in may 2D projected map?


This is the map I am working with: http://www.jetplan.com/weather/data/maps/eutball06.gif

What I am trying to achieve is to map a (lat,lon) to a (x,y) pixel on that image.

I think the map is an Albers projection.

I have used the code mentioned above to get an x and y value.

My problem is that the (x,y) coordinates I get are related to a unit sphere and I am not sure how am I supposed to map this to a pixel on the image of the map.


1 Answer 1


To use any formula, you need the parameters of the Albers Equal Area projection:

latitude and longitude of origin
first and second parallel

You can guess the longitude from the only meridian that is straightly vertical, but the others are more difficult to get.

You might be better off by using a georeferencing tool. The georeferencer inside QGIS does a good job.

To get the real pixel address, follow the linked questions on the right.

  • The one crucial parameter that is missing from this answer is the radius of the sphere. Because the formulas referenced in the question are for a spherical datum, it is not clear which radius is intended.
    – whuber
    Commented May 12, 2015 at 17:20
  • I have tried QGIS and its georeferencer. It works very well and is very easy to use. I have transformed the albers projection into mercator. Now I can calculate pixels for given lat and lon using software I used for other projects. Thanks again! Commented May 13, 2015 at 8:12

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