National Oceanic and
Atmospheric Administration
United States Department of Commerce

Map projection aspect ratios

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 plotsinvolving map projections. Especially when using sub-global regions,the aspect ratio of the plot needs to be adjusted so that gridcells 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 ratiowithout setting it:

yes? go mp_aspect 0
The appropriate aspect ratio is 0.45607