Actually, looking back at results in my answer, this bilinear is "somewhat" strange (and other interpolation methods are probably useless for the given task).

pdl> $x = sequence 3,3

pdl> $y = zeroes 5,5

pdl> bilin2d( $x, $y )

pdl> p $y

[
 [  0 0.5   1 1.5   2]
 [1.5   2 2.5   3 3.5]
 [  3 3.5   4 4.5   5]
 [4.5   5 5.5   6 6.5]
 [  6 6.5   7 7.5   8]
]
[download]

That's better now. We can even visualize it with mesh3d [$y].

karthik248, it's not clear what kind of plot do you mean? 3-D? Over-impose some visualization onto a world map? Or just 2-D image with 3 different colors?

Thanks for the update. I meant a 2-D image with RGB or ARGB.

use strict;
use warnings;
use PDL;
use PDL::IO::Image;

# data
my $x = sequence( 100, 100 );

# ranges
my $range1 = $x < 3000;
my $range2 = ( $x >= 3000 ) * ( $x <= 7000 );
my $range3 = $x > 7000;

my $bytes = (     $range1 
            + 2 * $range2
            + 3 * $range3 )-> byte;

my $palette = byte [ 
    [  0,   0,    0 ],
    [ 255,  50,  50 ],
    [ 128, 255,   0 ],
    [ 255, 215,   0 ]
];

$bytes-> wimage( 'test.png', { palette => $palette });
[download]

Not sure if I understand what you need, but, "from the top of my head", this code produces rather dull looking image with three colorful stripes (no time to invent some "smart" data). You have your conditions, combine them, associate with palette of the same length + 1.