At Nuro, we have been working on developing scalable maps for many years now, and many of these tools have been used to enable multi-city driverless deployments. As the scale of our deployments and operating domain grows over time, limitations that were once rare become more frequent, and methods that work at a smaller scale are replaced with more general approaches that are more flexible. A perfect example of this is HD mapping and the challenges in growing and maintaining an HD map over time.