polskalokalnie/.agents/skills/remotion-maps/techniques/maptiler/references/map-geo-prep.md

Map Explainer — basemap & geo prep

How the basemap is cleaned and how ../scripts/prep-geo.mjs bakes the per-country data the component reads.

Basemap styling — strip the clutter

On load, remove the basemap's labels and inner admin borders so only your geography reads:

for (const l of m.getStyle().layers as any[])
  if (l.type === "symbol" || /other border/i.test(l.id)) m.removeLayer(l.id);

• type === "symbol" → every place/water/road label (the "MapTiler labels"). Gone.
• Inner admin-border layer IDs vary by style. Inspect the loaded style, remove state/province/district layers as needed, and retain only the context borders the production requires.
• Logo/attribution: maptilerLogo:false + attributionControl:false aren't always enough — also hide via CSS in the component:

  <style>{`.maplibregl-ctrl-bottom-left,.maplibregl-ctrl-bottom-right,.maplibregl-ctrl-attrib,.maptiler-logo{display:none!important}`}</style>
  

../scripts/prep-geo.mjs → outputs

Reads a routed river GeoJSON + country polygon GeoJSONs; writes:

• River line — simplified for a smooth draw. For a braided river, route one source→mouth path through the network first: greedy endpoint-chaining bounces between parallel channels. → src/geo/river-flow.json.
• public/geo/borders.geojson — each country's polygon tagged {country: name} (one source, filtered per country for the fills).
• src/geo/country-meta.json — per country { stop, anchor, border }.

stop — when a country lights up

Walk the river points; first point inside a country (turf.booleanPointInPolygon) = the arc-length fraction where the river enters it. Drives the trigger time. The headwaters country = 0.

anchor — label centre via pole of inaccessibility

The most-interior point of the country (clipped to a per-country story bbox so a big country centres in the relevant region, not its far bulge), then a small operator nudge. Pole = grid-sample inside the polygon, keep the point with max distance to the boundary. Centroids get pulled to edges — don't use them.

const pole = (poly) => {
  const bb = turf.bbox(poly), edge = turf.polygonToLine(poly), N = 46;
  let best = null, bestD = -1;
  for (let i = 0; i <= N; i++) for (let j = 0; j <= N; j++) {
    const p = turf.point([bb[0]+(bb[2]-bb[0])*i/N, bb[1]+(bb[3]-bb[1])*j/N]);
    if (!turf.booleanPointInPolygon(p, poly)) continue;
    const d = turf.pointToLineDistance(p, edge);
    if (d > bestD) { bestD = d; best = p.geometry.coordinates; }
  }
  return best;
};
const ANCHOR_BBOX = { china:[82,27,96,32], india:[76,14,99,31], bangladesh:[86,20,93,27] };  // story regions
const NUDGE = { china:[0,0.6], india:[-1.0,0], bangladesh:[0,-0.6] };                          // operator-directed

border — complete source geometry

Preserve every exterior ring from the named country source. Never clip a country or bilateral border to the framed bbox and never discard an off-screen segment: the geometry may leave the frame naturally. The renderer handles a MultiLineString by cumulative length, so it remains one timed reveal without inventing joins across gaps.

Tuning the geo prep for a new scenario

Want	Knob
Which countries	the country list in prep-geo.mjs (+ supply their polygon GeoJSONs)
Label centred in the right region	ANCHOR_BBOX[country] (the story bbox)
Nudge a label	NUDGE[country] (lng, lat offset)
What border is drawn	the complete named source geometry; never the visible extent
When each lights up	derived from stop — depends on the river geometry