Cambridge GIS "is all about Cambridge spatial data. We are constantly working on creating, maintaining, and delivering to our users the most accurate and reliable GIS datasets we can. We supply datasets, services, and applications to City staff, as well as to visitors to our website and other departmental sites which host our maps and apps. This site is a portal not only to interactive mapping applications, static map sets, mobile GIS, Cambridge GIS data downloads, and our GIS data dictionary, but it also has unique tools for exploring Cambridge through our custom address specific dashboard called myCambridge."
It is a huge resource and includes some historic data, but is mostly about current data.