Galactic SF III

Poul Anderson wrote many works about interstellar travel and three novels about intergalactic travel. James Blish wrote a tetralogy whose volumes are successively interplanetary, interstellar, intergalactic and inter-cosmic. Blish is comparable to Anderson but with a much smaller output.

Since both wrote galactic sf, I wondered how much information either of them imparted about the structure of the galaxy. Blish describes both a photograph and a model. See previous post. He also recounts this exchange over the instantaneous Dirac communicator:

"'EARTH POLICE AA EMERGENCY ACOLYTE CLUSTER CONDENSATION XIII ARM BETA...SYSTEM UNDER ATTACK BY MASS ARMY OF TRAMP CITIES. POLICE AID URGENTLY NEEDED. LERNER LIEUTENANT FORTY-FIFTH BORDER SECURITY GROUP ACTING COMMANDER CLUSTER DEFENSE FORCES. ACKNOWLEDGE.'"
-Cities In Flight (New York, 1981), pp. 394-395.

"'LERNER ACOLYTE DEFENSE FORCES YOUR MESSAGE IN. SQUADRON ASSIGNED YOUR CONDENSATION ON WAY. HANG ON. BETA ARM COMMAND EARTH.'" (p. 395)

This tells us something about police, defense and galactic structures. The Acolyte Cluster is in the thirteenth condensation of the second spiral arm. I know that stars form from condensation of primordial elements but nowhere else have I seen "condensation" used to describe a part of the galaxy. Here, a condensation is intermediate between a cluster and an arm.