# The formulas for the Apianus II Map-Projection

I like that you give the formula for the X-coordinate of a point on the Apianus II map, in terms of latitude. But, in the denominator, outside the square-root, shouldn’t that be Pi squared instead of just Pi?

X = 2*Lambda/Pi^2 * Sqrt(Pi^2 / 4 - phi^2)

And why not give the formula for the Y coordinate in terms of latitude:

Y = phi/Pi.

…where latitude (phi) & longitude (Lambda) are in radians, & the coordinates are expressed in terms of the height of the elliptical Apianus II map.

are you referring to Apian's globular projections / Torben Jansen | Observable ?

Yes, that’s the article that I’m referring to. I was pleased that that formula was given, but I wanted to mention the correction that was needed.

Apianus II is a simple, easily defined & explained, but attractive & realistic world-map.

@RumplestiltskinCarto This is a user contributed notebook, and the author is unlikely to notice your post here. I recommend to leave a comment on the notebook itself and/or submit a suggestion with your corrections.

That was the first thing I tried, but I couldn’t find an option for suggestions or comments. This forum was the only place I could find at the website for saying anything.

So I’d certainly appreciate any information about a suggestions or comments option that I missed.

I thought I’d looked everywhere, but I could have missed it.

This is part of Observable’s notebook functionality itself. If you hover your mouse over left edge of a cell, you should see an icon popup that you can click on to leave a comment. Of course, you need to be signed in to do so.

Having said that, I do see a `π * π` in the code. Not that I know anything about this particular projection.