Solved this one.

What I needed was another attribute to allow the user specify his/her wishes. The default is the same as above (ie. pass the x and y values to current file as parameters).

Within the image_map() method I have changed the line:

$coordinates .= sprintf $AREA_FORMAT, $xcoord, $ycoord, "$action_file?
+x=$xvalue&y=$yvalue", "Value: [$xvalue, $yvalue]", "Value: [$xvalue, 
+$yvalue]";
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To:

$coordinates .= sprintf $AREA_FORMAT, $xcoord, $ycoord, $self->get_act
+ion->($i);
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I have also changed $AREA_FORMAT accordingly:

my $AREA_FORMAT  = qq(<area shape=circle coords="%.3f, %.3f, 2" %s>\n)
+;
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The user has to ensure his/her subroutine takes one integer as an argument ($i - the current index) and returns a string. That way (s)he can iterate over a number of arrays, hard coded into his subroutine and associate the values correctly.

As an example, the following code:

#!/usr/bin/perl -w
use strict;
use GnuplotImageMap;

# generate some values to plot
my @xvalues = map { sprintf "%.3f", rand } 1 .. 10;
my @yvalues = map { sprintf "%.3f", rand } 1 .. 10;

# this is to test the "action"
my $alphabets = [ 'a' .. 'z' ];

# generate the image map
my $object = GnuplotImageMap->new(
    xvalues     => [@xvalues],
    yvalues     => [@yvalues],
    # this is where you specify what you want to do ... the default is
+ as before!
    action      => sub { my ($i) = @_; return $alphabets->[$i] || "out
+ of bounds here"; },
);

# print out the image map
print "\n\nThe image map:\n\n", $object->image_map(), "\n";

exit 0;
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Gives the following output:

The image map:

<img src="C:\DOCUME~1\ionyia\LOCALS~1\Temp\LSPVfXDptt.png" usemap="#PL
+OT">
<map name="PLOT">
<area shape=circle coords="605.000, 172.167, 2" a >
<area shape=circle coords="308.779, 207.111, 2" b >
<area shape=circle coords="588.668, 264.256, 2" c >
<area shape=circle coords="70.000,  310.300, 2" d >
<area shape=circle coords="397.195, 82.133,  2" e >
<area shape=circle coords="249.647, 370.322, 2" f >
<area shape=circle coords="273.863, 425.000, 2" g >
<area shape=circle coords="544.179, 162.300, 2" h >
<area shape=circle coords="598.805, 55.000,  2" i >
<area shape=circle coords="332.432, 269.189, 2" j >
</map>
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Note the alphabets: increasing from 'a' to 'j' in the image map string :)

UPDATE:
Tried to clarify the changes made and their effect on the output.