  We introduce the modular and scalable design of Kartta Labs, an open source,
open data, and scalable system for virtually reconstructing cities from
historical maps and photos. Kartta Labs relies on crowdsourcing and artificial
intelligence consisting of two major modules: Maps and 3D models. Each module,
in turn, consists of sub-modules that enable the system to reconstruct a city
from historical maps and photos. The result is a spatiotemporal reference that
can be used to integrate various collected data (curated, sensed, or
crowdsourced) for research, education, and entertainment purposes. The system
empowers the users to experience collaborative time travel such that they work
together to reconstruct the past and experience it on an open source and open
data platform.
