Latitude divides the optical-interconnect design space into five scales: waveguides with roughly 0.5 µm core cross-sections; device libraries with footprints of around 10–500 µm; optical engines in the 10–25 mm range; packages in the 50–80 mm range; and finally the rack, at roughly two meters. Its central idea is straightforward: from waveguide to rack, each physical scale sets constraints for the next one; from rack back to waveguide, measured device behavior must continuously be used to recalibrate the models.