  We introduce a layout similarity measure designed to evaluate the results of
layout generation. While several similarity measures have been proposed in
prior research, there has been a lack of comprehensive discussion about their
behaviors. Our research uncovers that the majority of these measures are unable
to handle various layout differences, primarily due to their dependencies on
strict element matching, that is one-by-one matching of elements within the
same category. To overcome this limitation, we propose a new similarity measure
based on optimal transport, which facilitates a more flexible matching of
elements. This approach allows us to quantify the similarity between any two
layouts even those sharing no element categories, making our measure highly
applicable to a wide range of layout generation tasks. For tasks such as
unconditional layout generation, where FID is commonly used, we also extend our
measure to deal with collection-level similarities between groups of layouts.
The empirical result suggests that our collection-level measure offers more
reliable comparisons than existing ones like FID and Max.IoU.
