Celestial Atlas vs Portolan Chart
星図の様式 / ポルトラーノ海図
Both sit in Diagrammatic Expression, so the question is not what they belong to but how they behave. Both are read here as style. They are reached for with some of the same intent, which is where they get confused.
Celestial Atlas
The Baroque celestial atlas layering constellation mythology over observation. Cellarius's Harmonia Macrocosmica marks the summit of an age when scientific diagram could also be decorative art.
Portolan Chart
A medieval working sea chart, crossed by radiating rhumb lines. Coastlines and place names run precisely along the vellum while flags and monsters fill the empty water, from a time when a map's usefulness and its ornament had not yet parted.
| Celestial Atlas | Portolan Chart | |
|---|---|---|
| Era | 17th–19th century | 13th–17th century |
| Family | Diagrammatic Expression | Diagrammatic Expression |
| Kind | Style | Style |
| Cues | Myth figures over stars / Concentric celestial structure / Gold and blue coloring / Ornamented cartouches | Radiating rhumb lines / Names perpendicular to coasts / The vellum ground / Flags and monsters as ornament |
| Best used for | Double-page plates for books and exhibitions on astronomy or navigation · Showing a whole body of knowledge on one sheet with its ornament intact | Books and exhibitions telling the story of routes or trade as a map · Ornamental maps whose real subject is the memory held in place names |
| Type | Title inside an ornamented frame, star names tiny and italic | Names packed perpendicular to the coast, key ports raised in red |
| Composition | Concentric spheres at the center, four corners filled with cartouches | Several compass roses with straight lines radiating across the sheet |
| Material | Gold and hand color on deep blue, stars struck as engraved points | Black and red on a vellum ground, flags and monsters in open water |
| Caution | Drawing the myth figures so large that the star positions vanish leaves a plate working neither as diagram nor as ornament. | Drawing rhumb lines as pattern while ignoring how they answer the roses gives ornament that no longer looks like an instrument of navigation. |