Basic OpenIndexMap support

Closes #8

Author: thatbudakguy

src/index.html

@@ -117,6 +117,14 @@ <h1>OpenGeoMetadata Viewer Preview</h1>
         >
           Temperature (Points, GeoJSON)
         </button>
+        <button
+          data-record-url="https://raw.githubusercontent.com/OpenGeoMetadata/edu.stanford.purl/b74664cbb36fb985fe2ebee8d0d6d9657f06ada1/metadata-aardvark/zy/089/tj/2215/geoblacklight.json"
+        >
+          Peatland (Index Map, Polygons)
+        </button>
+        <button data-record-url="https://gist.githubusercontent.com/thatbudakguy/dcf881807aea33739a8cbb8fcefa42d0/raw/67b80876bdd17c21d654024bc77a1e4ece8a7fb6/hopkins.json">
+          Hopkins (Index Map, Points)
+        </button>
         <button
           data-record-url="https://raw.githubusercontent.com/OpenGeoMetadata/edu.stanford.purl/b74664cbb36fb985fe2ebee8d0d6d9657f06ada1/metadata-aardvark/cg/357/zz/0321/geoblacklight.json"
         >

src/lib/sources.ts

@@ -112,6 +112,7 @@ const getRecordSource = async (record: OgmRecord): Promise<AddSourceObject | und
       // Methods that create new sources are added here in order of preference
       // The first one that returns a valid source will be used
       await recordPMTilesSource(record),
+      recordIndexMapGeoJSONSource(record),
       recordGeoJSONSource(record),
       recordWMSSource(record),
       recordTMSSource(record),
@@ -172,6 +173,23 @@ const recordGeoJSONSource = (record: OgmRecord): AddSourceObject | undefined =>
   };
 };
 
+// Given a record, create a MapLibre GeoJSON source from an index map URL, if possible
+const recordIndexMapGeoJSONSource = (record: OgmRecord): AddSourceObject | undefined => {
+  // If no index map reference, nothing to do
+  const indexMapUrl = record.references.indexMapUrl;
+  if (!indexMapUrl) return;
+
+  // Create a GeoJSON source with the record's ID and attribution
+  return {
+    id: record.id,
+    source: {
+      type: 'geojson',
+      data: indexMapUrl,
+      attribution: record.attribution,
+    },
+  };
+};
+
 // Given a record, create a PMTiles source, if possible
 const recordPMTilesSource = async (record: OgmRecord): Promise<AddSourceObject | undefined> => {
   // If no PMTiles reference, nothing to do