This example displays a map with a set of geographic features loaded from a CartoDB SQL query, which returns data in GeoJSON format. The visualization uses the Leaflet mapping library to render the map and a `L.geoJson` layer to draw the features. Each feature is processed with an `onEachFeature` callback that assigns a `cartodb_id` property to the corresponding Leaflet layer and adds it to a `drawnItems` layer group, which is then added to the map. The data source is the `leaflet_data` table from the osm2 CartoDB account.