A tiny library to load common GeoJSON formats in Processing

geohelper.js

// A function that helps plot various GeoJSON to the canvas. This does not
// cover every type and use case, but may be a useful reference.
// See also: https://mappa.js.org/
function drawGeoJson(json_data, palette='white') {

  // Iterate every feature
  json_data.features.forEach((feature, ix) => {

    // Make sure that we have a properly formatted file
    if (typeof feature.geometry !== 'object' ||
        typeof feature.geometry.coordinates !== 'object') {
            console.error("Not in GeoJSON format!")
            console.log(feature);
            return;
    }

    let coordinates = feature.geometry.coordinates;

    // Set a single color, or pick the next in an array of colors
    fill(typeof palette == 'string' ? palette : palette[ix % palette.length])

    coordinates.forEach((shapegroup) => {

      if (feature.geometry.type == 'Polygon') {
        drawShape(coordinates);
      } else if (feature.geometry.type == 'MultiPolygon') {
        coordinates.forEach((polygroup) => {
          drawShape(polygroup);
        });
      } else if (feature.geometry.type == 'Point') {
        drawPoints(coordinates);
      } else {
        console.warn('Unknown geometry type:', feature.geometry);
      }

    }); // -coordinates
  }); // -features
} // -drawGeoJson

// We will use this function to draw a polygon shape
function drawShape(shapegroup) {
  shapegroup.forEach((shape) => {
    beginShape();

    shape.forEach((coordinate) => {
      // Calculate the projection
      let pos = projection(coordinate);
      if (pos[0] == NaN) {
        console.warn("NaN in shape!")
        return;
      }
      vertex(pos[0], pos[1]);
    });

    endShape();
  }); // -shapegroup
}

// An example point drawer, which you can replace with your own
function drawPoints(pointgroup, color, label=false) {
  pointgroupo.forEach((point) => {
    noStroke();
    fill(color);
    // Calculate screen pixels
    let pos = projection(point);
    if (pos[0] == NaN) {
      console.warn("NaN in point!")
      return;
    }
    // Draw a circle and optional label
    circle(pos[0], pos[1], 3)
    if (label) {
      text(feature.properties.name, pos[0] + 3, pos[1] + 3);
    }
  });
}