P-velocity 3-dimensional mantle model BDP98 (Boschi & Dziewonski, JGR, 1999).
Approximately equal area block model (5 degrees X 5 degrees X 193.3 km).
The model consists of 15 layers, numbered 01 through 15, 01 being the
shallowest and 15 the deepest.
(bdp98.ps is a postscript file with an overall picture of the whole model;
layer 01 is at the top to the left, layer 02 is right of 01, and so on,
down to layer 15 wich is at the bottom to the left. The color scale
saturates at +-1% at all depths.) 

The layers are given in the files layer_01.d through layer_15.d, in 
the following format (example):

      1.25403E-02
   0.    85.0000
   0.    90.0000
     90.0000    90.0000
     90.0000    85.0000
   -0.301233
     90.0000    85.0000
     90.0000    90.0000
     180.000    90.0000
     180.000    85.0000
   -0.391459
     180.000    85.0000
     180.000    90.0000
     270.000    90.0000
     270.000    85.0000

the single numbers are the value of the PERCENT velocity perturbation
relative to PREM within each block; the following four pairs of numbers
are longitude and latitude of the four vertices of the corresponding
block... and so on...


I believe that the best way to plot this file is to use gmt.
First you need to write a program to turn each file into something like:

> -G165/243/172
   0.    85.0000
   0.    90.0000
     90.0000    90.0000
     90.0000    85.0000
> -G255/184/101
     90.0000    85.0000
     90.0000    90.0000
     180.000    90.0000
     180.000    85.0000
> -G255/162/071
     180.000    85.0000
     180.000    90.0000
     270.000    90.0000
     270.000    85.0000

where the three integers after -G, separated by /, define the color
corresponding to the velocity perturbation in the block (and then
the block-vertices coordinates are just the same), based on a colorscale
of your choice.
Assuming that you called this new file image, you can use (more or less)
the commands

psxy image -JH180/6 -Bg45/g45 -R0/360/-90/90 -K -M >! fig.ps 
pscoast -R0/360/-90/90 -O -JH180 -W1 -Dc -A5000 >> velocity.ps

to obtain a figure with that layer of the model (and the coastline).

note: the files layr___a.d.gz through layr___o.d.gz contain the same
layers (a being 01, b being 02 and so on), in the format x,y,z, 
x and y being 1-degree spaced points (64800 records for each file),
and z being the model.

Lapo Boschi, Cambridge, September 10, 1999.

boschi@seismology.harvard.edu