What is a layer defined as

Question

Hello, I'm reading through the documentation for the Hierarchical Layout algorithm and I'm trying to determine what exactly a "layer" is defined as, since it doesn't appear anywhere previously in the help documentation.

Use Hierarchical layout style to highlight the main direction or flow within a directed graph. Cyclic dependencies of nodes will be automatically detected and resolved. Nodes will be placed in hierarchically arranged layers. Additionally the ordering of the nodes within each layer is chosen in such a way that the number of line (or edge) crossings is small. 

A precise definition would be very nice to have, since Layers is a tab appearing in so many layout algorithm settings.

Thank you,

~Jaime

Answer 1

The meaning of layer depends on the context it appears in but it typically refers to a collection of nodes that are more or less aligned on an imaginary vertical or horizontal line. For hierarchical layout, a more detailed description with some example images is here: http://docs.yworks.com/yfiles/doc/developers-guide/incremental_hierarchical_layouter.html