Within a company, levels codify the hierarchy, scope & responsibility of employees. The question we try to answer with our mapping is: "If an employee at company X were to switch to company Y, which level would they come in at?". The answer then is: what is the equivalent scope / responsibility across companies. There's several other factors (company size, interview performance, etc) that go into actual leveling when you switch companies and thus we really emphasize that this is a rough guide. I think we've settled on something that's generally agreeable for most folks. We constantly take feedback though and adjust based on what we hear from users switching between companies.