def save(path, prefix = '')
      FileUtils.mkdir_p(path)
      @edge_tab.save(File.expand_path(prefix + 'edges.tab', path))
      @node_tab.save(File.expand_path(prefix + 'nodes.tab', path))
    end
def save(path, prefix = '')
      FileUtils.mkdir_p(path)
      @edge_tab.save(File.expand_path(prefix + 'edges.tab', path))
      @node_tab.save(File.expand_path(prefix + 'nodes.tab', path))
    end
Create a layer from an edge tab and a node tab
 @param edge_tab [Table]
 @param node_tab [Table]
 Save the layer to disk
 @param path [String] path to output directory
 @param prefix [String]