Here's an update after a few evenings of stippling! I finished the skeleton for one spiral arm, and I'm making sure to give it a ragged edge as it fades toward the outer limits of the galaxy so that there's both a more interesting appearance and a more evocative terrain to the map.

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This spiral arm consists largely of the Sea of Relics and Far Reaches regions, relatively unpopulated parts of the galaxy that are rich in the ancient civilization's ruined megastructures. Over the millennia, gravitational tides and radiation degradation have slowly ripped many of the ancient planetary-scale structures into drifting pieces. Research institutions throughout the galaxy investigate the relics to determine their original purposes and recover ancient knowledge. Entrepreneurial-minded scavengers also comb the fields of derelicts for valuable technology and raw materials to sell.

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Ruined megastructures are not the only landmarks in the galaxy. Stellar objects and astrophysical phenomena dominate the starscape in places. Here is line art for The Menagerie, a star-forming nebula in the Erhn territory of the Imperium of the Triumvirate:

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I'm planning to do a pass over the other spiral arm next, and then move through the galaxy expanding the stippled shape (especially in the central region). For now, my goal is to establish the overall form.