If you took all the covers from the Offical Handbook of the Marvel Universe, and strung them together, you’d get this beautiful poster.

“The poster is based off the first Marvel Handbook. The first 12 issues of the Handbook could be put together to form a poster.

The MU poster you bought came out I believe in 1988. The poster was modified to include characters that have appeared in the Deluxe Edition handbook like Asp, Firestar, Ego, Hellions, Yellowjacket (De Mara), Black Crow, Longshot, Volcana, Spider-Woman (Julia Carpenter), Phoenix (Rachel Summers), among others.

The poster also modified the costumes of some characters that were already there like Nomad, Beast, Angels, Cyclops, Paladin, Dazzler, Iron Man, and Magneto.”
from here