How to write contour figure on world map

Dear All.

I want to write contour figure on world map.
I have seen the tutorial/graphics/earth.C.
“MERCATOR” option makes contour figure.
When another contour figure draw same canvas, the world map is filled by the other figure.
How to write the contour figure on world map?

And I have another question.
Why the Y axis of “MERCATOR” figure is -2.5 to 2.5?

Any help with this issue would be greatly appreciated.
Thank you.

It is not possible right now to draw the contour values a number on a contour plot. It can be done with a macro in some cases. With mercator projection it is more complex because you need to do the transformation in this special coordinate system. Regarding the Y axis value I guess it is the Mercator algorithm which does that. There is nothing special in the macro.