Tile Schema

tile57's vector tiles use a fixed set of layers and fields. The generated MapLibre style depends on this schema, so the names are a contract. Do not rename a layer or a field without updating the style generator (src/style/maplibre.zig) to match and bumping the schema version.

This vocabulary is versioned as tile57/2. The tiles and the portrayal assets are generated from the same S-101 catalogue and stamped with that schema_version, so a renderer can refuse a schema it doesn't speak. Any change to a layer name or field key bumps it.

Every tile uses an extent of 4096 and a buffer of 64.

Live path coverage

Whether the tiles come from a pre-baked PMTiles archive or are generated live from a raw S-57 chart, the schema is the same. The live path (src/scene/) emits areas, area_patterns, lines, point_symbols, soundings, and text. Features carrying SCAMIN (attr 133) keep it as the per-feature scamin property, and every feature has a display_priority for S-52 fill ordering. DEPCNT lines carry valdco (the contour value, including the 0 m drying line) for line-centre labels. The same schema is encoded as MLT or MVT (see architecture).

Color is always a name

Fields like color_token and halo_color_token hold S-101 color names, not RGB values. The style resolves them against colortables.json to get the right Day, Dusk, or Night color — which is how a renderer switches palette without regenerating tiles.

Zoom levels and navigational bands

A nautical chart is not one map at one scale. NOAA compiles each chart (an ENC cell) for a navigational purpose — from a wide overview to a close-in berthing plan — and the right chart to show depends on how far you are zoomed in. Each chart carries a compilation scale (CSCL, a 1:N denominator) that maps to a band, and each band covers the Web-Mercator zoom range that matches its scale:

Band	Zoom range
Overview	5 – 8
General	8 – 10
Coastal	10 – 12
Approach	12 – 14
Harbor	14 – 16
Berthing	16 – 18

Vector tiles scale crisply, so a renderer overzooms the top level rather than baking more. Within a band, a feature may carry an S-52 SCAMIN (the scale below which it should disappear) as the per-feature scamin property; the style hides the feature once the display is coarser than 1:scamin, so minor features drop out at their own thresholds and the chart never clutters. (Earlier schema versions split these into separate *_scamin layers; tile57/2 folds them back into the base layers, gated by the per-feature property.)

The six layers

Every feature also carries shared metadata the style and the pick report read, regardless of layer:

Field	Type	Meaning
class	string	S-57 object-class acronym.
cell	string	Source chart stem.
s57	string	The feature's full S-57 attribute set as a JSON object (the pick report).
display_priority	int	S-52 draw priority (fill/stroke ordering).
cat	int	Display category (base / standard / other gating).
band	int	Navigational band rank.
scamin	int	SCAMIN 1:N denominator — present only on features that carry one.

bnd, pts, plane, vg, and the date_* keys are additional gating properties emitted only when relevant. The layer-specific fields follow.

areas

Filled polygons, such as depth areas and land.

Field	Type	Meaning
color_token	string	Fill color name.
drval1, drval2	number	Depth-range min/max for depth areas (DEPARE/DRGARE).
oscl	int	Overscale denominator, present when the chart shows finer than its compilation scale.

area_patterns

Polygons filled with a repeating pattern instead of a flat color.

Field	Type	Meaning
pattern_name	string	Name of the fill pattern.
oscl	int	Overscale denominator, as above.

lines

Stroked lines, such as depth contours and coastline. Symbolized/complex line runs and sector-light legs fold in here too.

Field	Type	Meaning
color_token	string	Stroke color name.
width_px	number	Stroke width in pixels.
dash	string	Dash pattern (empty = solid).
valdco	number	Contour value for DEPCNT lines (including the 0 m drying line), for line-centre labels.
ls_style	string	Complex line-style name (symbolized lines).
ls_arc0	number	Sector-arc start bearing (sector-light legs).

point_symbols

Single symbols placed at a point, such as buoys and beacons.

Field	Type	Meaning
symbol_name	string	Name of the symbol.
rotation_deg	number	Rotation in degrees.
rot_north	int	1 = hold the symbol north-up (line-placed and point symbols).
scale	number	Scale factor.
danger_depth, sym_deep	number, string	Isolated-danger depth + the deep-water symbol variant (the DANGER01/DANGER02 swap).

soundings

Depth soundings, drawn as digit glyph strings (SNDFRM digit composition).

Field	Type	Meaning
sym_s, sym_g	string	Bold + faint digit glyph strings, in metres.
sym_s_ft, sym_g_ft	string	The same glyph strings, in feet.
depth	number	Sounding depth in metres.

text

Text labels (the name typically derives from OBJNAM via the featureName attribute).

Field	Type	Meaning
text	string	The label text.
font_size_px	number	Font size in pixels.
color_token	string	Text color name.
halo_color_token	string	Halo color name ("" = no halo).
halo_width	number	Halo width in pixels (0 = none).
halign, valign	string	Horizontal and vertical alignment.
loff	string	Pixel offset "ux,uy" from the anchor, present only when nonzero.
tgrp	int	S-52 text viewing group.