isom-maplibre

A MapLibre GL style that renders orienteering maps per ISOM 2017-2, the IOF International Specification for Orienteering Maps, at 1:10,000.

Every line width, dash, pattern and symbol is computed from the ISOM dimensions (mm at 1:15,000, enlarged ×1.5 and converted at 96 dpi), uses the ISOM colours, and is stacked in the ISOM colour order. The dimensions come from ISOM 2017-2 itself: the symbol definitions of section 3, the precise definitions of section 3.8, and the colours of Appendix 1 (CMYK printing and colour definitions). The colour order is the IOF's table for ISOM 2017-2 in "IOF Map Specifications - Printing and Colour Definitions" (2022, the successor of Appendix 1): olive above the greens, streams above the contours, contours above lakes.

Install

npm install @metsa/isom-maplibre maplibre-gl

Releases are published to npm with provenance.

Usage

In-memory GeoJSON

isomGeojsonStyle() returns the GeoJSON style (one GeoJSON source per table, no sprite) with your data attached, and registerIsomIcons() supplies the pattern and symbol images at runtime:

import maplibregl from "maplibre-gl";
import { isomGeojsonStyle, registerIsomIcons } from "@metsa/isom-maplibre";

const map = new maplibregl.Map({
  container: "map",
  style: isomGeojsonStyle({ contours, water, paths }), // FeatureCollections, lng/lat
});
registerIsomIcons(map);

Tables you leave out start empty; fill them later with map.getSource(table).setData(featureCollection). DETAIL_TABLES lists them. The style without data is also exported as @metsa/isom-maplibre/style.geojson.json.

Vector tiles

import style from "@metsa/isom-maplibre/style.json";

The style reads one vector source per table from /tiles/<table> (TileJSON) and its images from the sprite /sprite/isom. Point those URLs at your server and build the sprite from ICONS (SVGs keyed by image id), or pass -sprites to the generator (see Development). Two optional sources serve large tile sets:

• overview: one source whose layers carry vegetation_areas, water, paths and manmade, drawn below zoom 13 in place of the per-table sources.
• coverage: polygons outlining where data exists. From zoom 10 they are white paper under the map, so a basemap merged underneath never shows through; below zoom 10 they are a translucent brown patch marking where maps are.

Every layer except the background carries metadata for selecting layers without parsing ids: isom:pass (detail, overview or coverage), and on symbol layers isom:code and isom:group (the ISOM colour group). The style's own metadata["isom:tables"] lists the tables in definition order.

Data

Each feature carries a string isom_code property. Codes without a symbol stay invisible.

| Table | Geometry | isom_code | |--------------------|-----------------|----------------------------------------------------------------------| | contours | lines | 101.000, 101.001 (slope line), 102.000, 103.000, 104.000, 105.000 | | cliffs | lines, polygons | 201.000, 202.000, 206.000 | | knolls_points | points | 109.000, 111.000 | | vegetation_areas | polygons, lines | 401.000 to 410.000, 412.000, 413.000, 415.000 | | water | lines, polygons | 301.000, 302.000, 304.000, 305.000, 306.000, 308.000 | | paths | lines | 502.000 to 507.000 | | manmade | lines, polygons | 501.000, 509.000, 510.000, 511.000, 515.000, 516.000, 520.000, 521.000, 521.001 (large building: outline and 50% infill), 529.000 |

A 101.001 slope line is a two-point line from the contour downhill; the symbol takes its bearing from it. Coordinates are lng/lat, as for any MapLibre source.

Scale

Up to zoom 15 every dimension is constant; above it the whole map magnifies ×2 per zoom level, which keeps ISOM proportions intact. Zoom 15 is true 1:10,000 at about 56° latitude. At latitude φ the true-scale zoom is log2(156543.03 · cos φ / 2.6458).

Limitations

MapLibre cannot draw some ISOM ornaments, so these symbols are simplified:

• Plain line without its ornament: 104 tags, 105 dots, 201 tags, 510 pylon bars, 515 dots, 516 tags, 529 tick pairs.
• Flat fill without its pattern: 402 and 404 holes, 412 dots, 413 dot rows.
• Dashes are not balanced per feature as ISOM asks.
• The white core of 509 and 511 masks what lies beneath it.
• Fill patterns (308, 407, 409) keep their density above zoom 15.
• The map must be displayed north-up for the north-oriented patterns to be correct.

Development

isom.yaml defines the whole style: scale, palette (referenced through YAML anchors), images, and the symbol stack. It is validated by isom.schema.json, which editors with the YAML language server pick up automatically; the generator enforces the schema too, plus the cross-references it cannot express (palette colours, table and image names). src/style.json, src/style.geojson.json and src/icons.json are generated from it:

go generate ./...   # regenerate src/
go test ./...       # schema, ISOM dimension and colour-order checks
npm run build && npm test

The generator is also usable directly, for example to write a sprite directory for a tile server. It reads the definition embedded in the module unless -spec names another file:

go run github.com/MetsaApp/isom-maplibre/cmd/genstyle@latest \
  -style style.json -geojson-style style.geojson.json -icons icons.json -sprites sprites/

Go programs get the parsed definition from isomstyle.Default() in github.com/MetsaApp/isom-maplibre/pkg/isomstyle (Load and Parse take another one), and render it with Style, GeojsonStyle and Icons.

Commits follow Conventional Commits; release-please opens the release PR, and merging it tags the release and publishes the package.

License

MIT. ISOM is a specification of the International Orienteering Federation; this project is not affiliated with the IOF.