MapLabels.svg.svelte component

<!--
  @component
  Adds SVG text labels based features in the data or a custom GeoJSON Feature Collection.
 -->
<script>
  import { getContext } from 'svelte';

  const { data, width, height } = getContext('LayerCake');

  /**
   * @typedef {Object} Props
   * @property {Function} projection - A D3 projection function. Pass this in as an uncalled function, e.g. `projection={geoAlbersUsa}`.
   * @property {Function} getLabel - An accessor function to get the field to display.
   * @property {number|undefined} [fixedAspectRatio] - By default, the map fills to fit the $width and $height. If instead you want a fixed-aspect ratio, like for a server-side rendered map, set that here.
   * @property {Function} getCoordinates - An accessor function to get the `[x, y]` coordinate field. Defaults to a GeoJSON feature format.
   * @property {Array<Object>|undefined} [features] - A list of labels as GeoJSON features. If unset, the plotted features will defaults to those in `$data.features`, assuming this field a list of GeoJSON features.
   */

  /** @type {Props} */
  let { projection, getLabel, fixedAspectRatio, getCoordinates, features } = $props();

  let fitSizeRange = $derived(fixedAspectRatio ? [100, 100 / fixedAspectRatio] : [$width, $height]);

  let projectionFn = $derived(projection().fitSize(fitSizeRange, $data));
</script>

<g class="map-labels">
  {#each features || $data.features as d}
    {@const coords = projectionFn(getCoordinates(d))}
    <text class="map-label" x={coords[0]} y={coords[1]}>{getLabel(d)}</text>
  {/each}
</g>

<style>
  .map-labels {
    pointer-events: none;
  }
  .map-label {
    color: #333;
    /**
     * If you render this in an ScaledSvg layout component, you'll
     * want to make this like 1px bc it's actually being zoomed by about 10x
     */
    font-size: 8px;
    text-anchor: middle;
  }
</style>