Salish Sea basemap

A basemap of the Northeast Pacific coast, from Monterey Bay to Haida Gwaii, built from open data for SalishSea.io and Orcasound. It keeps showing depth and shoreline at the zooms where Esri's ocean tiles go blank, and it is drawn so that the coloured dots of whale sightings stay the most visible thing on the map.

It is published at tiles.salishsea.io as a MapLibre style and the vector tiles it draws from, with image tiles and lists of place names beside them.

The newest version is 2026.10.22:

• A page linking every file of the version: https://tiles.salishsea.io/2026.10.22/index.html
• Style: https://tiles.salishsea.io/2026.10.22/style.json
• A page for trying it out, with and without its relief: https://tiles.salishsea.io/2026.10.22/viewer/index.html?right=flat
• Image tiles, for stitching into a picture: https://tiles.salishsea.io/images/c271f1d11804c054/{z}/{x}/{y}.webp
• Place names of water bodies and points, from the US and Canadian gazetteers: https://tiles.salishsea.io/places/places-gazetteers-6ebc4b7473854290.json
• Place names of islands, cities, towns, villages and ferry terminals, from OpenStreetMap, under the ODbL: https://tiles.salishsea.io/places/places-osm-c2e7cd37c8651122.json
• Place names, regions: https://tiles.salishsea.io/places/places-regions-e25c8dde585a7200.json

The image tiles and place lists are named for their contents, not for a version, so that a version that doesn't change them shares the earlier version's files. Their URLs can't be guessed from a version number. Each version's release links a page that lists them, for versions after 2026.10.13, and each version's style names them in its metadata. To read them from any version:

curl -s https://tiles.salishsea.io/2026.10.22/style.json | jq .metadata

The pictures in this README are drawn from the build by make pictures (CONTRIBUTING), so they show the map as it is.

Using it

Point a MapLibre map at a version's style. The style reads its tiles from PMTiles archives, so register the pmtiles protocol first:

import maplibregl from 'maplibre-gl';
import { Protocol } from 'pmtiles';

maplibregl.addProtocol('pmtiles', new Protocol().tile);
const map = new maplibregl.Map({
  container: 'map',
  style: 'https://tiles.salishsea.io/2026.10.22/style.json',
  center: [-123.1, 48.5], zoom: 9,
  minZoom: 3, maxBounds: [[-180, 15], [-90, 70]],
});

• Pin a version. A published version never changes, so a page that names one always draws the same map, and every file can be cached for a year. A new version gets a new number, in CalVer: 2026.10.1, then 2026.10.2, then 2026.11.1. The versions are this repository's tags, each on the commit that built it (decision 007).
• Any site may use it. Every response allows any origin.
• Keep to the coverage. The coast's detailed layers cover 136–120°W, 36–54.8°N, from zoom 5. Around them, and below zoom 5, a coarse map from GEBCO covers 180–90°W, 15–70°N, so the minZoom and maxBounds above keep a map where there is always something drawn (decision 012).
• It is in Web Mercator, like the tiles of most web maps. MapLibre's globe projection draws it on a sphere instead, which shows Alaska at its true size beside California when zoomed out; but at zoom 3 the globe shows the edge of the coarse map's coverage, which maxBounds doesn't hide there (decision 013).
• Draw your data on top. Layers you add after the style loads go above everything in it, labels included, which is where sightings belong.
• Turn the relief off on a slow device: map.setLayoutProperty('relief', 'visibility', 'none'). The relief is the light and shadow of the seafloor and land, shaded by the browser.
• Keep the attribution. The style credits its sources, which MapLibre's attribution control shows, including that the map is not for navigation; the depth grids are credited once, for both the depths and the relief. Archives derived from OpenStreetMap are under the ODbL.

Everything the style needs, the labels' fonts and the icons included, is served from tiles.salishsea.io, so a page that uses it needs to allow only that one site (010). Image tiles, for things that stitch tiles into a picture rather than draw a map, such as SalishSea.io's preview cards, are drawn from the same style without its labels. A version's style names them in its metadata, as salishsea:images: a URL with {z}, {x} and {y} in it, in 256-pixel tiles, as Esri's are, each drawn at 512 pixels for high-density screens. They cover zooms 0 to 5 over the coarse map's area, zooms 6 to 10 over the coast and a little past it, and zooms 11 to 15 only along the Salish Sea's shore (decision 014).

Place names, for a search that takes people to a place on the map, are named in the metadata under salishsea:places, and the newest version's are linked above: the URLs of two JSON lists, gazetteers and osm, of the Salish Sea's places that a search offers, about 2,100 in all. One holds the larger water bodies and points from the two gazetteers. The other holds the larger islands, cities, towns, villages and ferry terminals from OpenStreetMap, under the ODbL. Each list states its sources and licence, then gives each place as a row of its columns: the name, its kind, a longitude and latitude to look at, a zoom to look from (MapLibre's, which counts 512-pixel tiles), and any other names it goes by. The OpenStreetMap list also says, under gazetteer_islands, which island each of the gazetteers' places that shares its name with another is on, to tell them apart; it is found from OpenStreetMap's outlines, so it is kept there (decision 018).

What it shows

The San Juan Islands at zoom 9.4. The coloured dots stand in for whale sightings, in SalishSea.io's colours.

• Depth is tinted in bands, darker where deeper, with labelled isobaths; the deepest band, from 2000 m, runs to the seafloor's lowest point.
• Ground that dries at low tide, such as the mud flats of Boundary Bay, is khaki (004).
• Relief shades the seafloor and the land lightly, and fades out by zoom 13, before it would blur (002).
• Land is one flat colour, so that sightings stand out, except parks, state parks among them, in a faint green: many are where people watch from shore. Rivers and streams are blue (003). A large park is named at its headquarters or visitor centre, if it has one (026).
• Ferry routes are dashed, from zoom 9, because many casual sightings are made from ferries (005).
• Landmarks people steer by: lighthouses, tall radio and television towers, and what the charts mark as conspicuous from the water, each with an icon and, closer in, its name (015).
• Places people watch from, such as beaches, parks, nature reserves, marinas and ferry terminals, are named from OpenStreetMap; shops, restaurants and other businesses are not (016).
• Peninsulas are named from a zoom set by their size, Key Peninsula from 7 and Miller Peninsula from 8 (023).
• Salmon runs at the mouth of each named river that reaches the sea, such as "Chinook (spring, summer, fall) · coho · chum (fall)", because resident killer whales follow salmon (020).
• Shipping lanes and two-way routes, faintly outlined from zoom 8, with precautionary areas dashed, arrows for their direction from 10 and names such as "Northbound lane" from 12, as reports name them. They are left out of the image tiles (019).
• Bays, straits, channels and points are named from the US and Canadian government gazetteers, and the boundary at sea is drawn (006).
• Water regions, one for each water name the map labels, covering the water, are in the tiles but drawn only when a page shows them: set water_regions_fill and water_regions_line to visible. A version's metadata names them as a list too, regions under salishsea:places, each region's name as a card would say it, "Mud Bay (Sucia Island)" where several share it, and base as the map labels it (027).

Lime Kiln Point at zoom 14, where Esri's ocean tiles show "Map data not yet available". The relief has faded out, and the isobaths and depth bands carry the seafloor.

The Skagit at zoom 10, where a salmon river reads as plainly as the interstate beside it.

Off Victoria at zoom 10.6: the Strait of Juan de Fuca's lanes meet Haro Strait's, under the sightings.

The Skagit's runs at zoom 10.6, labelled where its South Fork reaches the flats of Skagit Bay.

What it is built from

Layer	Source	Terms
Land, roads, places, water outlines	Protomaps daily build of OpenStreetMap	ODbL
Ferry routes	The same Protomaps extract, redrawn so that each channel has one line at low zooms (005)	ODbL
Depth labels' typeface	Noto Serif, from the Noto project (017); the other labels' fonts and the icons are Protomaps' (010)	SIL Open Font Licence
Landmarks	OpenStreetMap, from Geofabrik's extracts (015); icons from Maki	ODbL; icons public domain (CC0)
Names of bays, straits, channels and points on the US side	USGS Geographic Names Information System, placed and timed against the depth grid (006)	Public domain
The same on the Canadian side	Natural Resources Canada's Canadian Geographical Names Database	Open Government Licence – Canada
Salmon and steelhead runs on each river	WDFW and the Northwest Indian Fisheries Commission's SWIFD in Washington; Fisheries and Oceans Canada's NuSEDS in British Columbia (020)	"Open for public consumption"; Open Government Licence – Canada
Shipping lanes	NOAA's ENC Direct wherever NOAA charts, including Haro Strait and Boundary Pass; Fisheries and Oceans Canada's Vessel Traffic Routes where it doesn't (019)	Public domain; Open Government Licence – Canada
Water regions, one per water name the map labels, covering the water from 42°N to 51.5°N (027)	The names above; Natural Resources Canada's outlines and NOAA's ENC Direct named sea areas and land; British Columbia's terrestrial boundary; the depth grids and drying ground below	Public domain; Open Government Licence – Canada; Open Government Licence – British Columbia
The Canada–US boundary at sea	NOAA's maritime limits and boundaries	Public domain
Depths and relief wherever Canada's grid has data: north of about 48.06°N, which takes in the Strait of Juan de Fuca, Haro Strait, the San Juan Islands and the north end of Admiralty Inlet	Natural Resources Canada's West Coast topo-bathymetric DEM, resampled from 10 m to 30 m	Open Government Licence – Canada
Depths and relief everywhere else near the coast, including Puget Sound, Hood Canal and the Washington coast	NOAA's Coastal Relief Model, 1 arc-second (about 30 m)	Public domain
Depths in the deep ocean, beyond those grids; and, averaged to about 2.5 km, the coarse map of the whole Northeast Pacific shown zoomed out and past the coast's edges	GEBCO's global grid, 15 arc-seconds (about 450 m) (009, 012)	Public domain

Canada's grid is preferred because NOAA's shows straight seams where its survey patches meet. The two measure height from different levels, so Canada's depths read 1–2 m shallower; each is kept as published, except within 4 km of a grid's edge, where it is blended with the grid beneath (001, 009).

Anything derived from OpenStreetMap is kept in archives and lists of its own, so that the ODbL's share-alike terms don't reach the public-domain and Canadian data. The map is not for navigation.

Why one 30 m grid, and why not the Canadian Hydrographic Service's own depths, is in SalishSea.io's decision 073. Why the basemap is its own project is in 074. Decisions made since are in decisions/.

Contributing

How to build the map, draw this README's pictures and publish a version is in CONTRIBUTING.md.

Licence

Code is MIT; documentation and the style are CC BY 4.0. Built tiles carry their sources' terms (above). See LICENSE.