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"Early maps only showed a few well-known features like the 'Pillars of Hercules' (the modern Straits of Gibraltar) or the island of Sicily. Once the map was outlined in terms of its major features, succeeding generations of mapmakers filled in the details. . . . Similarly, the concentric designer begins by sketching out the main features, based on the key constraints, and then successively elaborates these until the details are crystallized."

(Expert Systems for Experts by Parsay & Chignell, p. 53)