Return to Ferret FAQ

Map projection aspect ratios

Question:

How can I get the right aspect ratio for a plot when I'm using
a map projection and a sub-global region?

Example:

Explanation:

Ferret's default aspect ratio is inappropriate for most plots involving map projections. Especially when using sub-global regions, the aspect ratio of the plot needs to be adjusted so that grid cells in the plot that should be square actually are.

An additional map projection script, mp_aspect.jnl, is provided which calculates and sets the appropriate aspect ratio. It should be run after you have run the map projection script.

Solution:

The example graphic above was created with the following commands:

yes? use coads_climatology
yes? set region/x=140:240/y=40:70/l=1
yes? set grid sst
yes? go mp_bonne
yes? go mp_aspect
yes? shade/noaxis sst, x_page, y_page
yes? go mp_fland 20

Note: You can also determine the aspect ratio without setting it:

yes? go mp_aspect 0
The appropriate aspect ratio is 0.45607