function streetsToGraph(streets) {
  let graph = createGraph(),
    streetToGraphBound = streetToGraph.bind(this, graph);

  //For each street, get an array of indices for the start, intersections, and end coordinates, in order from
  //start to end. Then, add the coordinates at each index as a node, and an edge between each adjacent node in the array,
  //associating the distance between the nodes (between their coordinates) with each edge.
  streets.eachLayer(streetToGraphBound);

  return graph;
}
Convert a layerGroup of streets into a graph. Useful if you modify the street layers during the simulation
and want routing to work with the new street network.

@param {LayerGroup} streets - A Leaflet layerGroup of streets, forming a street network.
@returns {Object} - A graph representing the street network, operable by the ngraph pathfinder.