graphical display of routes

I've been thinking of how to solve the "problem" of knowing what adresses
are routed or not in our IGP.

Does anyone know of a utility that you can feed a "show ip route ospf" or
perhaps via snmp someway, that'll display what part of the IP space there
is a route for or not, perhaps divided by /24 or /19 or something.

What I was thinking of was to create a gif, with one pixel per IP number,
so a /30 route would show up as a 4 pixel line etc. A /19 would then be a
block of 256 times 32 pixels, where one can fairly easily see what IPs are
being routed or not. It seems to be a common problem that link nets come
and go and are not being reused....

Any good ideas?