Depth areas, isobaths, and soundings compiled per zoom level

Depth areas and isobaths are now compiled per zoom tier, the way an ENC is compiled per usage band, and the soundings follow chart practice for selection and rounding.

Chart fixes

• Depth areas and isobaths compiled per zoom (#195). Each zoom tier (z6, z7 to 8, z9 to 10, z11 to 12, z13 and up) is its own complete partition, cut from the bathymetry at that tier's resolution with the isobath ladder a chart draws at that scale. Zooming out can only shoal, never deepen, and bands too small to read at a tier's scale merge into their shallower neighbour. A coarse source viewed closely shows its own content rather than 2 m bands interpolated from kilometre cells. The emphasized safety contour follows the ladder drawn at each zoom.
• Low-zoom isobaths keep their shape (#210). At z6 to z9 the lines had been thinned to long straight segments across shelves and island arcs; they now keep a vertex per pixel and draw with round joins.
• No more false shallow water along ditches and small canals (#196). Under coarse sources, polder ditches and canals narrower than the source's own cell had read as 0 to 2 m depth bands with soundings on them (the Haarlemmermeer). Water narrower than the source cell now stays land in that source and shows as unknown depth.
• Exact datum is unknown water, never foreshore (#195). A depth of exactly 0 is the land sentinel and the fill for water a source holds no depth for; it no longer draws as drying.
• Unknown-depth water fills no longer compound (#195). Abutting water polygons inside a lake had overlapped into a dark lattice along every outline; the fills now dissolve per tile.
• Soundings in line with chart standards (#180). The selection keeps the least depths a chart ranks first (the 1 m floor that discarded real shoals is gone), rounds toward the shoal side, and thins by the chart's spacing rules.
• No more horizontal stripes across the map at fixed latitudes (#192). Unknown-water rows on the easternmost tiles had wrapped around the antimeridian.

Pipeline

• Depth-area tier files declare their full read sets, so a bbox smoke and a planet build heal the same stems (#195); the vector archive's census measures each feature at its own tier's zoom (#195); a bundle whose tiles overflowed fails instead of merging bands (#210).
• Depth-area contouring uses upstream GDAL's fast polygon mode (#193); the planet build aborts early when the box's disk can't hold the run (#178) and stops a doomed build sooner (#194); a GEOS overlay failure on one stem no longer stops the planet (#208).

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