Shallow seas split into depth bands at low zoom

Shallow seas no longer turn into one solid blue band at low zoom, and Bands mode is a compiled chart partition from z4 up.

Chart fixes

• Shallow seas split at 10, 20 and 50 m at low zoom (#214). The coarse tiers carried no isobath shallower than 50 m (z7 to 8) or 200 m (z6), so a shallow sea like the Kattegat or the North Sea painted one band in the darkest tint. Each tier now follows NOAA's ENC Design Handbook contour set for its scale, plus the 10 and 20 m contours wherever that set lacks them.
• Bands mode and isobaths start at z4 (#214). A new z4 tier with the Overview contour set replaces the raster handoff at z5, so the shelf no longer changes tint between z5 and z6.
• Isobaths follow the seabed at z7 to z10 (#214). Each tier is cut one zoom finer than before and keeps a vertex per pixel at the last zoom it serves. At z8 over the Kuril arc the median segment went from 6.4 to 3.9 px.
• Depth bands below 4,000 m and in the deepest trenches (#214). Water deeper than a tier's deepest contour got no band at all: the deep ocean at z4 to z6, and trenches past 10,000 m or 5,000 fathoms at every zoom. A floor below the deepest ocean closes it.
• Shoal soundings show with their ring (#214). A least depth inside a 10 to 100 m contour now shows from the zoom that contour draws at.

Pipeline

• Coarse tiers reuse the native tier's tidal-water union, the cost that dominated the slowest stems: the Arctic stem 4-3-3-8 went from 316 to 101 minutes (#214).
• The low-zoom vector bundle writes below its top zoom at detail 11, so the Philippines z4 tile fits under tippecanoe's size ceiling (#215).
• Every commit that touches the style or viewer gets a viewer preview, and the style package now releases from style-v* tags once the live tiles carry its pipeline (#213).

Seascape is not an official Electronic Navigational Chart and is never a replacement for one. Not for navigational use.