OK, so it's the (string) values of another variable. In gretl terms, these are called "observation markers" or labels, if I'm not totally missing something. As I wrote before, please see ch. 6 in the guide, subsection "Displaying data labels", which deals explicitly with scatter plots.I am talking about adding the values of a qualitative variable, e.g. country codes, as labels.
As an example from my megacity research, imagine a scatter plot of carbon footprint (y-axis) vs city population (x-axis). In such a plot, it would be very useful if the data points were labeled with the megacity name.
No it's not. I also wrote before that string-valued series may be what you want, and there's an entire chapter in the user guide (unless you are using a severely outdated gretl version).
So I am suggesting that two separate improvements be considered for gretl:
(1) Add the capability of handling qualitative (i.e. text) variables, something that is sorely missing right now.
(2) Add the capability of adding a qualitative variable as labels of the points of a scatter plot.
See above. To start with, data menu / add observation labels. And/or the "markers" command, which also allows you to use a strings array as your source object. I admit it may be a bit confusing to keep "variable labels" and "observation labels" (== markers) apart. (Internal note: maybe we should avoid the term observation labels in the documentation and replace it with obs markers to match the command name.)
cheers
sven