internal long WriteTo(Stream stream)
{
var p = stream.Position;
// write header and version.
stream.WriteWithSize($"{nameof(Graph)}");
stream.WriteByte(1);
// writes zoom and edge data size.
stream.WriteByte((byte)_zoom);
stream.WriteByte((byte)_edgeDataSize);
// write tile index.
stream.WriteByte((byte)TileSizeInIndex);
_tiles.CopyToWithHeader(stream);
// write vertices.
stream.WriteByte((byte)CoordinateSizeInBytes);
stream.Write(BitConverter.GetBytes((long)_vertexPointer), 0, 8);
_vertices.CopyToWithSize(stream);
_edgePointers.CopyToWithSize(stream);
// write edges.
stream.Write(BitConverter.GetBytes((long)_edgePointer), 0, 8);
_edges.CopyToWithSize(stream);
// write shapes.
_shapes.CopyTo(stream);
return(stream.Position - p);
}